Lane change assist apparatus for vehicle

ABSTRACT

A driving support ECU initializes a target trajectory calculation parameter at a start of LCA; calculates, based on the target trajectory calculation parameter, a target trajectory function representing a target lateral position which is a target position of an own vehicle in a lane width direction in accordance with an elapsed time from the start of LCA; calculates a target control amount based on the target trajectory function; when a steering operation by a driver has been detected, again initializes the target trajectory calculation parameter; and recalculates the target trajectory function based on the target trajectory calculation parameter.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a lane change assist apparatus for avehicle configured to assist/support a steering operation for changinglanes.

2. Description of the Related Art

Conventionally, a lane change assist apparatus has been known which isconfigured to assist a steering operation (steering wheel operation) forchanging lanes. Such a lane change assist apparatus calculates a targettrajectory in such a manner that a vehicle changes a traveling directionof the own vehicle toward a lane (adjacent lane) being a destination ofchanging lanes. The lane change assist apparatus controls a steeringangle of right and left steered wheels in such a manner that the vehicletravels along the calculated target trajectory.

For example, an apparatus (hereinafter referred to as a “conventionalapparatus”) as proposed in Japanese Patent Application Laid-Open (kokai)2016-141264 A sets a target trajectory based on a time period which ittakes for a driver to move an own vehicle in a lateral direction (lanewidth direction) by a predetermined distance. The conventional apparatussets a trajectory distance of the target trajectory shorter as that timeperiod is shorter. When the target trajectory is set, the conventionalapparatus starts a lane change assist to control a steering amount insuch a manner that the own vehicle travels along the target trajectory.Therefore, the driver can have the own vehicle change lanes withoutoperating a steering wheel.

The conventional apparatus sets the target trajectory in accordance witha rotating speed of the steering wheel operated by the driver before thelane change assist is executed. However, while the lane change assist isbeing executed, the driver may perform an additional steering operation(that is, the driver may add/supplement a steering amount through amanual operation of the steering wheel to the steering amount controlledby the automatic steering control) because the driver wishes to completethe lane change in a shorter time. In this case, if the targettrajectory set at the start of the lane change assist is used until thecompletion of the lane change assist, the lane change may be performedaccording to a trajectory along which the driver does not intend totravel.

The present invention is made to cope with the problem described above.That is, one of objects of the present invention is to provide a lanechange assist apparatus which can have the own vehicle change lanesalong a trajectory reflecting the intention of the driver.

In order to achieve the above-mentioned object, according to oneembodiment of the present invention, there is provided a lane changeassist apparatus for a vehicle, including:

a lane recognition unit (12) for recognizing a lane to detect a relativepositional relationship of an own vehicle with respect to the lane;

a target trajectory calculation unit (10) for, based on the relativepositional relationship of the own vehicle with respect to the lane,calculating a target trajectory in such a manner that the own vehiclechanges lanes toward an adjacent lane; and

an assist control unit (10, 20) for executing/performing a lane changeassist control by controlling steering of a steered wheel in such amanner that the own vehicle travels along the target trajectory.

The lane change assist apparatus further includes a steering operationdetermination unit (S19) for determining whether or not a driver hasperformed a steering operation while the lane change assist control isbeing executed.

The target trajectory calculation unit includes:

a first calculation unit (S13, S14) for, at a start of the lane changeassist control, calculating the target trajectory along which the ownvehicle is to travel from the start of the lane change assist controluntil a completion of the lane change assist control; and

a second calculation unit (S22, S23) for, at a steering determinationtime point at which the steering operation determination unit determinesthat the driver has performed the steering operation, calculating thetarget trajectory along which the own vehicle is to travel from thesteering determination time point until the completion of the lanechange assist control, based on a lateral position which is a positionof the own vehicle in a lane width direction at the steeringdetermination time point, and a lateral movement state amountrepresenting a movement state of the own vehicle in the lane widthdirection at the steering determination time point.

the assist control unit is configured to

control the steering of the steered wheel in such a manner that the ownvehicle travels along the target trajectory calculated by the firstcalculation unit until the steering determination time point (at whichthe steering operation determination unit determines that the driver hasperformed the steering operation), and

control the steering of the steered wheel in such a manner that the ownvehicle travels along the target trajectory calculated by the secondcalculation unit after the steering determination time point (at whichthe steering operation determination unit determines that the driver hasperformed the steering operation) (S15 to S18).

In the lane change assist apparatus, the lane recognition unitrecognizes the lane and detects the relative positional relationship ofan own vehicle with respect to the lane. The lane is, for example, anarea sectioned by white lines. The target trajectory along which the ownvehicle travels can be determined by recognizing the lane. The targettrajectory calculation unit calculates the target trajectory for havingthe own vehicle change lanes toward the adjacent lane (which is a targetlane for lane change), based on the relative positional relationship ofthe own vehicle with respect to the lane. The assist control unitexecutes/performs the lane change assist control to control the steeringof the steered wheel in such a manner that the own vehicle travels alongthe target trajectory.

When the driver has performed the steering operation during the lanechange assist control, if the target trajectory set/determined at thestart of the lane change assist continues being used until thecompletion of the lane change assist as it is, the lane change may beperformed along a trajectory along which the driver does not intend totravel. Therefore, the lane change assist apparatus according to thepresent invention includes the steering operation determination unit.The steering operation determination unit determines/confirms whether ornot the driver has performed the steering operation while the lanechange assist control is being executed/performed. That is, the steeringoperation determination unit determines whether or not the driver hasoperated a steering wheel. In this configuration, the steering operationdetermination unit may determine that the driver has performed thesteering operation, when the driver has terminated the steeringoperation of the steering wheel.

The target trajectory calculation unit includes the first calculationunit and the second calculation unit. The first calculation unitcalculates, at the start of the lane change assist control, the targettrajectory along which the own vehicle is to travel from the start ofthe lane change assist control until/to the completion of the lanechange assist control. Further, the second calculation unit calculates,at the steering determination time point at which the steering operationdetermination unit determines that the driver has performed the steeringoperation, the target trajectory along which the own vehicle is totravel from the steering determination time point until/to thecompletion of the lane change assist control, based on the “lateralposition which is the position of the own vehicle in the lane widthdirection (road width direction) at the steering determination timepoint” and the “lateral movement state amount representing the movementstate of the own vehicle in the lane width direction at the steeringdetermination time point”.

The assist control unit is configured to

control the steering of the steered wheel in such a manner that the ownvehicle travels along the target trajectory calculated by the firstcalculation unit until the steering determination time point (at whichthe steering operation determination unit determines that the driver hasperformed the steering operation), and

control the steering of the steered wheel in such a manner that the ownvehicle travels along the target trajectory calculated by the secondcalculation unit after the steering determination time point (at whichthe steering operation determination unit determines that the driver hasperformed the steering operation).

In this manner, at the steering determination time point at which thesteering operation determination unit determines that the driver hasperformed the steering operation, the target trajectory is againdetermined/calculated (recalculated) based on the lateral position atthe steering determination time point and the lateral movement stateamount at the steering determination time point. Therefore, a suitabletarget trajectory can be determined/calculated in response to thebehavior of the own vehicle which is changed by the steering operationof the driver. The steering of the steered wheel is controlled based onthe suitable target trajectory. Accordingly, the own vehicle can be madeto change lanes along the target trajectory reflecting the intention ofthe steering operation performed by the driver.

In an aspect of the present invention, the first calculation unit isconfigured to calculate/determine, as the target trajectory (or as afunction which determines the target trajectory), a target trajectoryfunction representing/expressing a target lateral position which is atarget position of the own vehicle in the lane width direction inaccordance with a first elapse time from the start of the lane changeassist control, (for a period from the start of the lane change assistcontrol) until/to the completion of the lane change assist control, and

the second calculation unit is configured to calculate, as the targettrajectory (or as a function which determines the target trajectory), atarget trajectory function representing/expressing a target lateralposition which is a target position of the own vehicle in the lane widthdirection in accordance with a second elapse time from the steeringdetermination time point, (for a period from the steering determinationtime point) until/to until the completion of the lane change assistcontrol.

In the above aspect of the present invention, the first calculation unitis configured to calculate, as the target trajectory, the targettrajectory function representing/expressing the target lateral positionwhich is the target position of the own vehicle in the lane widthdirection in accordance with the first elapse time from the start of thelane change assist control (until the completion of the lane changeassist control). Further, the second calculation unit is configured tocalculate, as the target trajectory, the target trajectory functionrepresenting/expressing the target lateral position which is the targetposition of the own vehicle in the lane width direction in accordancewith the second elapse time from the steering determination time point(until the completion of the lane change assist control). Therefore, theassist control unit controls the steering of the steered wheel in such amanner that the lateral position of the own vehicle matches (becomesequal to) the target lateral position determined based on the targettrajectory function calculated by the first calculation unit until thesteering determination time point (at which the steering operationdetermination unit determines that the driver has performed the steeringoperation). Further, the assist control unit controls the steering ofthe steered wheel in such a manner that the lateral position of the ownvehicle matches (becomes equal to) the target lateral positiondetermined based on the target trajectory function calculated by thesecond calculation unit after the steering determination time point (atwhich the steering operation determination unit determines that thedriver has performed the steering operation). Therefore, the lateralposition of the own vehicle can be controlled in accordance with thefirst elapse time or the second elapse time. Accordingly, the ownvehicle can be made to change lanes along a desired trajectory.

In an aspect of the present invention, the assist control unit includes:

a target lateral state amount calculation unit (S15) for, based on thetarget trajectory function calculated by the first calculation unit orthe second calculation unit, successively/sequentially calculating atarget lateral state amount, the target lateral state amountrepresenting a target lateral position of the own vehicle at a currenttime point and a target lateral movement state amount which is a targetvalue of a movement state of the own vehicle in the lane width directionat the current time point;

a target yaw state amount calculation unit (S16) forsuccessively/sequentially acquiring a vehicle speed of the own vehicleat the current time point, and successively/sequentially calculating atarget yaw state amount which is a target value at the current timepoint related to a movement for changing a direction of the own vehicle,based on the vehicle speed and the target lateral movement state amount;and

a steering control unit (S17, S18) for controlling the steering of thesteered wheel based on the target lateral position and the target yawstate amount.

In the above aspect of the present invention, the assist control unitincludes the target lateral state amount calculation unit, the targetyaw state amount calculation unit, and the steering control unit. Thetarget lateral state amount calculation unit successively/sequentiallycalculates the target lateral state amount, based on the targettrajectory function calculated by the first calculation unit or thesecond calculation unit. The target lateral state amount represents thetarget lateral position of the own vehicle at the current time point,and the target lateral movement state amount which is the target valueof the movement state of the own vehicle in the lane width direction atthe current time point.

The lateral movement state amount includes, for example, a speed and/oracceleration in the lane width direction of the own vehicle. Forexample, by differentiating the target trajectory function with respectto time, a target lateral speed (speed in the lane width direction) ofthe own vehicle at an arbitrary time point can be acquired. Further, bysecond-order differentiating the target trajectory function with respectto time, a target lateral acceleration (acceleration in the lane widthdirection) of the own vehicle at an arbitrary time point can beacquired. Therefore, the target lateral movement state amount can becalculated by using the target trajectory function.

As the vehicle speed of the own vehicle is acquired, the target yawstate amount can be calculated, which is the target value related to themovement (movement for changing the direction of the own vehicle) andwhich is required to obtain the target lateral movement state amount ofthe own vehicle. Therefore, the target yaw state amount calculation unitsuccessively/sequentially calculates the target yaw state amount whichis the target value at the current time point related to the movementfor changing the direction of the own vehicle, based on the vehiclespeed and the target lateral movement state amount.

The steering control unit controls the steering of the steered wheelbased on the target lateral position and the target yaw state amount.That is, the steering control unit controls the steering of the steeredwheel in such a manner that the lateral position of the own vehiclematches (becomes equal to) the target lateral position and the yaw stateamount for changing the direction of the own vehicle matches (becomesequal to) the target yaw state amount.

According to the above aspect of the present invention, the own vehiclecan be made to change lanes smoothly while reflecting an acceleratorpedal operation performed by the driver (that is, change in the vehiclespeed).

In an aspect of the present invention, the first calculation unit isconfigured to calculate the target trajectory functionrepresenting/expressing the target lateral position which is the targetposition of the own vehicle in the lane width direction in accordancewith the first elapse time from the start of the lane change assistcontrol, based on:

(i) an initial lateral state amount representing a lateral position ofthe own vehicle at the start of the lane change assist control and alateral movement state amount which is a movement state of the ownvehicle in the lane width direction at the start of the lane changeassist control;

(ii) a final target lateral state amount representing a target lateralposition of the own vehicle at the completion of the lane change assistcontrol and a target lateral movement state amount of the own vehicle atthe completion of the lane change assist; and

(iii) a target lane change time period which is a target time periodfrom the start of the lane change assist control until the completion ofthe lane change assist control, and

Further, the second calculation unit is configured to calculate, thetarget trajectory function representing the target lateral position ofthe own vehicle in accordance with the second elapse time from thesteering determination time point, based on:

(i) a lateral state amount at the steering determination time pointrepresenting a lateral position of the own vehicle at the steeringdetermination time point and a lateral movement state amount of the ownvehicle at the steering determination time point;

(ii) the final target lateral state amount representing the targetlateral position at the completion of the lane change assist control andthe target lateral movement state amount at the completion of the lanechange assist control; and

(iii) a target lane change remaining time period which is a targetremaining time period from the steering determination time point untilthe completion of the lane change assist control.

In the above aspect of the present invention, the first calculation unitis configured to calculate the target trajectory functionrepresenting/expressing the target lateral position which is the targetposition of the own vehicle in the lane width direction in accordancewith the first elapse time from the start of the lane change assistcontrol, based on the initial lateral state amount, the final targetlateral state amount, and the target lane change time period. Theinitial lateral state amount represents the lateral position of the ownvehicle at the start of the lane change assist control and the lateralmovement state amount which is the movement state of the own vehicle inthe lane width direction at the start of the lane change assist control.Further, the final target lateral state amount represents the targetlateral position at the completion of the lane change assist control andthe target lateral movement state amount at the completion of the lanechange assist. In addition, the target lane change time periodrepresents the target time period from the start of the lane changeassist control until/to the completion of the lane change assistcontrol. The lateral movement state amount includes, for example, adetection value(s) of speed and/or acceleration in the lane widthdirection of the own vehicle. The target lateral movement state amountincludes, for example, a target value(s) of speed and/or acceleration inthe lane width direction of the own vehicle. The lateral position of theown vehicle and the lateral movement state amount of the own vehicle areobtained from the relative positional relationship of the own vehiclewith respect to the lane which is detected by the lane recognition unit.

On the other hand, the second calculation unit is configured tocalculate, the target trajectory function representing/expressing thetarget lateral position of the own vehicle in accordance with the secondelapse time from the steering determination time point (at which thesteering operation determination unit determines that the driver hasperformed the steering operation), based on the lateral state amount atthe steering determination time point, the final target lateral stateamount, and the target lane change remaining time period. The lateralstate amount at the steering determination time point represents thelateral position of the own vehicle at the steering determination timepoint and the lateral movement state amount at the steeringdetermination time point. The final target lateral state amountrepresents the target lateral position at the completion of the lanechange assist control and the target lateral movement state amount atthe completion of the lane change assist control. The target lane changeremaining time period is the target remaining time period from thesteering determination time point until/to the completion of the lanechange assist control.

Therefore, at the steering determination time point (at which thesteering operation determination unit determines that the driver hasperformed the steering operation), the target trajectory function can becalculated, which makes the actual lateral state amount smoothly varyfrom the lateral state amount at that time point. As a result, the ownvehicle can be made to change lanes in a smoother manner.

In an aspect of the present invention, the second calculation unit isconfigured to set the target remaining lane change time period based ona remaining distance at the steering determination time point which is adistance required for having the own vehicle move in the lane widthdirection until the completion of the lane change assist control.

In the above aspect of the present invention, the target remaining lanechange time period is set/determined based on the remaining distance atthe steering determination time point which is a distance required forhaving the own vehicle move in the lane width direction until thecompletion of the lane change assist control. Thus, ever if the driveroperates the steering wheel during the lane change assist control, asuitable target trajectory function can be calculated/determined.Accordingly, the own vehicle can be made to change lanes along thetarget trajectory while reflecting the intention of the steeringoperation performed by the driver in a more effective manner.

In an aspect of the present invention, the second calculation unit isconfigured to correct/modify the target remaining lane change timeperiod in such a manner that, the higher a lateral speed or lateralacceleration in the lane width direction of the own vehicle at thesteering determination time point is, the shorter the target remaininglane change time period is.

In the above aspect of the present invention, the target remaining lanechange time period is corrected/modified in such a manner that thetarget remaining lane change time period is shorter, as the lateralspeed of the own vehicle at the steering determination time point or thelateral acceleration in the lane width direction of the own vehicle atthe steering determination time point is higher. Therefore, a suitabletarget trajectory function can be calculated. Accordingly, the ownvehicle can be made to change lanes along the target trajectory whilereflecting the intention of the steering operation performed by thedriver in a more effective manner.

In an aspect of the present invention, the second calculation unit isconfigured to calculate the target trajectory function up to once (thatis, only once) during one (that is, a single consecutive) lane changeassist control (S30).

During the lane change assist control, the steering operationdetermination unit may determine that the driver has performed thesteering operation a plurality of times. If the target trajectoryfunction is calculated/updated for each steering determination timepoint to control the steered wheel, the behavior of the own vehicle maybe unstable. In view of this, in the above aspect of the presentinvention, the number of calculations of the target trajectory functionis limited to up to once during one lane change assist control (that is,a period from the start of the lane change assist control to thecompletion of that lane change assist control). Consequently, the ownvehicle can be made to change lanes stably.

In an aspect of the present invention, the second calculation unit isconfigured to

at the steering determination time point, calculate a deviation betweenthe “target lateral position of the own vehicle obtained by the targettrajectory function calculated by the first calculation unit” and an“actual lateral position of the own vehicle detected by the lanerecognition unit”, and

when the deviation (i.e., a magnitude of the deviation) is equal to orhigher than a threshold and the actual lateral position is positioned ata position deviated/shifted in a lane change direction with respect tothe target lateral position, calculate the target trajectory function(S31, S32, S33).

When the driver has performed the steering operation during the lanechange assist control, and if the actual lateral position of the ownvehicle does not greatly deviate from the target lateral position in thelane change direction, the target trajectory function calculated at thestart of the lane change assist control may be used as it is (it may becontinued being used). Therefore, in the above aspect of the presentinvention, at the steering determination time point at which thesteering operation determination unit determines that the driver hasperformed the steering operation, the second calculation unit calculatesthe deviation between the “target lateral position of the own vehicleobtained by the target trajectory function calculated by the firstcalculation unit” and the “actual lateral position of the own vehicledetected by the lane recognition unit”. When the deviation is equal toor higher than the threshold and the actual lateral position ispositioned at the position deviated/shifted in the lane change directionwith respect to the target lateral position, the second calculation unitcalculates the target trajectory function again. Therefore, the targettrajectory function is not calculated (to be switched) more thannecessary. Consequently, the own vehicle can be made to change lanesstably. In addition, the calculation load of the second calculation unitcan be suppressed low.

In an aspect of the present invention, the steering operationdetermination unit is configured to determine that the driver hasperformed the steering operation, when a steering torque input/appliedto a steering wheel by the driver becomes equal to or higher than afirst threshold for determining a start of the steering operation andthereafter becomes equal to or lower than a second threshold fordetermining a termination of the steering operation (S191 to S196).

In the above aspect of the present invention, when the steering torqueinput to a steering wheel by the driver becomes equal to or higher thanthe first threshold and then becomes equal to or lower than the secondthreshold, the steering operation determination unit determines that thedriver has performed the steering operation. The first threshold is athreshold for determining the start of the operation of the steeringwheel performed by the driver. The second threshold is a threshold fordetermining the termination of the operation of the steering wheelperformed by the driver. Therefore, the second threshold is lower thanthe first threshold. Consequently, it can be easy to determine that thedriver has performed the steering operation.

In the above description, references used in the following descriptionsregarding embodiments are added with parentheses to the elements of thepresent invention, in order to assist in understanding the presentinvention. However, those references should not be used to limit thescope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic configuration diagram for illustrating a lanechange assist apparatus for a vehicle according to an embodiment of thepresent invention.

FIG. 2 is a plan view for illustrating disposing positions ofsurrounding sensors and a camera sensor.

FIG. 3 is a diagram for illustrating lane-related vehicle information.

FIG. 4 is a diagram for illustrating actuation of a turn signal lever.

FIG. 5 is a flowchart for illustrating a steering assist control routineaccording to the embodiment.

FIG. 6 is a diagram for illustrating a trajectory of the vehicle.

FIG. 7 is a diagram for illustrating a target trajectory function.

FIG. 8 is a diagram for illustrating a target trajectory function.

FIG. 9 is a flowchart for illustrating a steering operationdetermination routine according to the embodiment.

FIG. 10 is a flowchart for illustrating a steering assist controlroutine according to a modified example 1.

FIG. 11 is a flowchart for illustrating a steering assist controlroutine according to a modified example 2.

DETAILED DESCRIPTION OF THE EMBODIMENTS

A lane change assist apparatus according to the present invention willnext be described with reference to the drawings.

The lane change assist apparatus according to the embodiment of thepresent invention is applied to a vehicle (hereinafter also referred toas an “own vehicle” in order to be distinguished from other vehicles).The lane change assist apparatus, as illustrated in FIG. 1, includes adriving support (assist) ECU 10, an electric power steering ECU 20, ameter ECU 30, a steering ECU 40, an engine ECU 50, a brake ECU 60, and anavigation ECU 70.

Those ECUs are electric control units each including a microcomputer asa main part, and are connected to one another so as to be able tomutually transmit and receive information via a controller area network(CAN) 100. The microcomputer herein includes a CPU, a ROM, a RAM, anonvolatile memory, an interface I/F, and the like. The CPU executesinstructions (programs and routines) stored in the ROM to realizevarious functions. Some or all of those ECUs may be integrated into oneECU.

Further, a plurality of types of vehicle state sensors 80 configured todetect a vehicle state and a plurality of types of driving operationstate sensors 90 configured to detect a driving operation state areconnected to the CAN 100. Examples of the vehicle state sensors 80include a vehicle speed sensor configured to detect a travel speed(hereinafter also referred to as a “vehicle speed v”) of the vehicle, afront-rear G sensor configured to detect an acceleration in a front-reardirection of the vehicle, a lateral G sensor configured to detect anacceleration in a lateral direction of the vehicle, and a yaw ratesensor configured to detect a yaw rate of the vehicle.

Examples of the driving operation state sensors 90 include anaccelerator operation amount sensor configured to detect an operationamount of an accelerator pedal, a brake operation amount sensorconfigured to detect an operation amount of a brake pedal, a brakeswitch configured to detect presence or absence of the operation on thebrake pedal, a steering angle sensor configured to detect a steeringangle, a steering torque sensor configured to detect a steering torque,and a shift position sensor configured to detect a shift position of atransmission.

Information (hereinafter, referred to as “sensor information”) detectedby the vehicle state sensors 80 and the driving operation state sensors90 is transmitted to the CAN 100. Each ECU can use the sensorinformation transmitted to the CAN 100 as appropriate. The sensorinformation may be information of a sensor connected to a specific ECU,and may be transmitted from the specific ECU to the CAN 100. Forexample, the accelerator operation amount sensor may be connected to theengine ECU 50. In this case, the sensor information representing theaccelerator operation amount is transmitted from the engine ECU 50 tothe CAN 100. For example, the steering angle sensor may be connected tothe steering ECU 40. In this case, the sensor information representingthe steering angle is transmitted from the steering ECU 40 to the CAN100. The same applies to the other sensors. Further, there may beemployed a configuration in which, without interpolation of the CAN 100,the sensor information is transmitted and received through directcommunication between specific ECUs.

The driving support ECU 10 is a control device serving as a centraldevice for performing driving support for a driver, and executes lanechange assist control, lane trace assist control, and adaptive cruisecontrol. As illustrated in FIG. 2, a front-center surrounding sensor11FC, a front-right surrounding sensor 11FR, a front-left surroundingsensor 11FL, a rear-right surrounding sensor 11RR, and a rear-leftsurrounding sensor 11RL are connected to the driving support ECU 10. Thesurrounding sensors 11FC, 11FR, 11FL, 11RR, and 11RL are radar sensors,and basically have the same configuration as each other except that thesensors have different detection regions. In the following, thesurrounding sensors 11FC, 11FR, 11FL, 11RR, and 11RL are referred to as“surrounding sensors 11” when the sensors are not required to beindividually distinguished from one another.

Each of the surrounding sensors 11 includes a radar transceiver (radartransmitting/receiving part) (not shown) and a signal processor (notshown). The radar transceiver radiates a radio wave in a millimeterwaveband (hereinafter referred to as a “millimeter wave”), and receivesa millimeter wave (that is, reflected wave) reflected by athree-dimensional object (e.g., other vehicles, pedestrian, bicycle, andbuilding) present within a radiation range. The signal processoracquires, every time a predetermined time period elapses, information(hereinafter referred to as “surrounding information”) representing, forexample, a distance between the own vehicle and the three-dimensionalobject, a relative speed between the own vehicle and thethree-dimensional object, and a relative position (direction) of thethree-dimensional object with respect to the own vehicle based on, forexample, a phase difference between the transmitted millimeter wave andthe received reflected wave, an attenuation level of the reflected wave,and a time period required from transmission of the millimeter wave toreception of the reflected wave. Then, the signal processor transmitsthe surrounding information to the driving support ECU 10. By using thesurrounding information, the driving support ECU 10 can detect (i) afront-rear direction component and a lateral direction component of thedistance between the own vehicle and the three-dimensional object, and(ii) a front-rear direction component and a lateral direction componentof the relative speed between the own vehicle and the three-dimensionalobject.

As illustrated in FIG. 2, the front-center surrounding sensor 11FC isdisposed at a front-center portion of a vehicle body, and detects athree-dimensional object present in a front region of the own vehicle.The front-right surrounding sensor 11FR is disposed at a front-rightcorner portion of the vehicle body, and mainly detects athree-dimensional object present in a front-right region of the ownvehicle. The front-left surrounding sensor 11FL is disposed at afront-left corner portion of the vehicle body, and mainly detects athree-dimensional object present in a front-left region of the ownvehicle. The rear-right surrounding sensor 11RR is disposed at arear-right corner portion of the vehicle body, and mainly detects athree-dimensional object present in a rear-right region of the ownvehicle. The rear-left surrounding sensor 11RL is disposed at arear-left corner portion of the vehicle body, and mainly detects athree-dimensional object present in a rear-left region of the ownvehicle.

In this embodiment, the surrounding sensors 11 are radar sensors, butother sensors such as clearance sonars and LIDAR (Laser ImagingDetection and Ranging) sensors can be employed instead.

Further, a camera sensor 12 is connected to the driving support ECU 10.The camera sensor 12 includes a camera unit and a lane recognition unit.The lane recognition unit analyzes image data obtained based on an imagetaken by the camera unit to recognize a white line(s) of a road. Thecamera sensor 12 (camera unit) photographs a landscape in front (ahead)of the own vehicle. The camera sensor 12 (lane recognition unit)supplies information on the recognized white line(s) to the drivingsupport ECU 10 every time a predetermined time period elapses.

The camera sensor 12 recognizes a lane which is a region sectioned bythe white lines, and detects a relative positional relationship of theown vehicle with respect to the lane based on a positional relationshipbetween the white lines and the own vehicle. Hereinafter, the “position”of the own vehicle means the position of the center of gravity. Further,a “lateral position” of the own vehicle to be described later means theposition of the center of gravity in the lane width direction. Inaddition, a “lateral speed” of the own vehicle means the speed of thecenter of gravity of the own vehicle in the lane width direction.Furthermore, a “lateral acceleration” of the own vehicle means theacceleration of the center of gravity of the own vehicle in the lanewidth direction. These are calculated and obtained based on the relativepositional relationship between the own vehicle and the white linesdetected by camera sensor 12. In the present embodiment, the position ofthe own vehicle refers to the position of the center of gravity, but itis not necessarily limited to the center of gravity position. Apredetermined specific position (for example, the center position of theown vehicle in plan view) of the vehicle may be adopted as the positionof the own vehicle.

As illustrated in FIG. 3, the camera sensor 12 sets/determines a lanecenter line CL corresponding to a center position in a width directionof the right and left white lines WL in a lane on/in which the ownvehicle is traveling. The lane center line CL is used as a target travelline in the lane trace assist control to be described later. Further,the camera sensor 12 calculates a curvature Cu of a curve of the lanecenter line CL.

Further, the camera sensor 12 calculates the position and the directionof the own vehicle in the lane sectioned by the right and left whitelines WL. For example, as illustrated in FIG. 3, the camera sensor 12calculates a distance Dy(m) in the lane width direction between theposition P of the center of gravity of the own vehicle C and the lanecenter line CL, that is, the distance Dy by which the own vehicle C isshifted (deviates) from the lane center line CL in the lane widthdirection. This distance Dy is referred to as a “lateral difference Dy”.Further, the camera sensor 12 calculates an angle formed between thedirection of the lane center line CL and the direction in which the ownvehicle C is facing/directing, that is, an angle θy(rad) by which thedirection in which the own vehicle C is facing/directing is shifted(deviates) in a horizontal plane direction from the direction of thelane center line CL. This angle θy is referred to as a “yaw angle θy”.When the lane is curved, because the lane center line CL is curved inthe same manner, the yaw angle θy is an angle formed between thedirection in which the own vehicle C is facing/directing and thedirection of a tangent line of this curved lane center line CL. In thefollowing, information (Cu, Dy, and θy) representing the curvature Cu,the lateral difference Dy, and the yaw angle θy is referred to as“lane-related vehicle information”. Regarding the lane-related vehicleinformation, the lateral direction (right and left direction) withrespect to the lane center line CL is specified by positive and negativesigns.

Further, every time a predetermined time period elapses, the camerasensor 12 also supplies, to the driving support ECU 10, informationrelating to the white lines, for example, the type of the detected whiteline (solid line or broken line), a distance (lane width) between theright and left adjacent white lines, and the shape of the white line, onnot only the lane of the own vehicle but also on adjacent lanes. Whenthe white line is a solid line, the vehicle is inhibited from crossingthe white line to change lanes. Otherwise, e.g., when the white line isa broken line (white line intermittently formed at certain intervals),the vehicle is allowed to cross the white line to change lanes. Thelane-related vehicle information (Cu, Dy, and θy) and the informationrelating to the white lines are collectively referred to as “laneinformation”.

In this embodiment, the camera sensor 12 calculates the laneinformation. Alternatively, the driving support ECU 10 may be configuredto analyze the image data transmitted from the camera sensor 12 toacquire/obtain the lane information.

Further, the camera sensor 12 can also detect a three-dimensional objectpresent in front (ahead) of the own vehicle based on the image data.Therefore, the camera sensor 12 may calculate and acquire not only thelane information but also front surrounding information. In this case,for example, there may be provided a synthesis processor (not shown)configured to synthesize the surrounding information acquired by thefront-center surrounding sensor 11FC, the front-right surrounding sensor11FR, and the front-left surrounding sensor 11FL and the surroundinginformation acquired by the camera sensor 12 to generate frontsurrounding information having a high detection accuracy. Thesurrounding information generated by the synthesis processor may besupplied to the driving support ECU 10 as the front surroundinginformation on the own vehicle.

A buzzer 13 is connected to the driving support ECU 10. The buzzer 13receives a buzzer sounding signal as input transmitted from the drivingsupport ECU 10 and produces a sound. The driving support ECU 10 soundsthe buzzer 13 when, for example, the driving support ECU 10notifies/informs the driver of a driving support situation, or when thedriving support ECU 10 alerts the driver.

In this embodiment, the buzzer 13 is connected to the driving supportECU 10, but the buzzer 13 may be connected to other ECUs, for example, anotification ECU (not shown) dedicated for notification, and the buzzer13 may be energized by the notification ECU. In this configuration, thedriving support ECU 10 transmits a buzzer sounding command to thenotification ECU.

Further, in place of or in addition to the buzzer 13, a vibrator fortransmitting vibration for notification for the driver may be provided.For example, the vibrator is provided to a steering wheel to vibrate thesteering wheel, to thereby alert the driver.

The driving support ECU 10 executes the lane change assist control, thelane trace assist control, and the adaptive cruise control, based on thesurrounding information supplied from the surrounding sensors 11, thelane information obtained based on the white line recognition by thecamera sensor 12, the vehicle state detected by the vehicle statesensors 80, the driving operation state detected by the drivingoperation state sensors 90, and the like.

A setting operation unit 14 to be operated by the driver is connected tothe driving support ECU 10. The setting operation unit 14 is anoperation unit for performing setting or the like regarding whether ornot to execute each of the lane change assist control, the lane traceassist control, and the adaptive cruise control. The driving support ECU10 receives a setting signal as input from the setting operation unit 14to determine whether or not to execute each control. In this case, whenthe execution of the adaptive cruise control is not selected, the lanechange assist control and the lane trace assist control are alsoautomatically set to be unexecuted. Further, when the execution of thelane trace assist control is not selected, the lane change assistcontrol is also automatically set to be unexecuted.

Further, the setting operation unit 14 has a function of inputtingparameters or the like representing the preference of the driver whenthe above-mentioned control is executed.

The electric power steering ECU 20 is a control device for an electricpower steering device. In the following, the electric power steering ECU20 is referred to as an “EPS ECU 20”. The EPS ECU 20 is connected to amotor driver 21. The motor driver 21 is connected to a steering motor22. The steering motor 22 is integrated/incorporated into a “steeringmechanism including the steering wheel, a steering shaft coupled to thesteering wheel, a steering gear mechanism, and the like” (not shown) ofthe vehicle. The EPS ECU 20 detects the steering torque that is input bythe driver to the steering wheel (not shown) with the steering torquesensor mounted in the steering shaft, and controls energization of themotor driver 21 based on the steering torque to drive the steering motor22. The assist motor is driven as described above to apply/add thesteering torque to the steering mechanism, and thus the steeringoperation of the driver is assisted.

Further, when the EPS ECU 20 receives a steering command from thedriving support ECU 10 via the CAN 100, the EPS ECU 20 drives thesteering motor 22 at a control amount specified by the steering commandto generate a steering torque. This steering torque represents a torqueto be applied to the steering mechanism in response to the steeringcommand from the driving support ECU 10, which does not require thedriver's steering operation (steering wheel operation) unlike a steeringassist torque to be applied for alleviating the driver's steeringoperation described above.

The meter ECU 30 is connected to a display unit 31 and right and leftturn signals 32 (meaning turn signal lamps and sometimes also referredto as “turn lamps”). The display unit 31 is, for example, amulti-information display mounted in front of a driver's seat, anddisplays various types of information in addition to values measured bymeters, for example, a vehicle speed. For example, when the meter ECU 30receives a display command in accordance with the driving support statefrom the driving support ECU 10, the meter ECU 30 displays a screeninstructed through the display command on the display unit 31. As thedisplay unit 31, in place of or in addition to the multi-informationdisplay, a head-up display (not shown) can also be employed. When thehead-up display is employed, it is preferred to provide a dedicated ECUfor controlling the display on the head-up display.

Further, the meter ECU 30 includes a turn signal drive circuit (notshown). When the meter ECU 30 receives a turn signal flashing commandvia the CAN 100, the meter ECU 30 intermittently flashes the turn signal32 arranged at a right or left position of the own vehicle according tothe turn signal flashing command. Further, while the meter ECU 30intermittently flashes the turn signal 32, the meter ECU 30 transmits,to the CAN 100, turn signal flashing information representing that theturn signal 32 is in an intermittently flashing state. Therefore, otherECUs can recognize the intermittently flashing state of the turn signal32.

The steering ECU 40 is connected to a turn signal lever 41. The turnsignal lever 41 is an operation unit for working (intermittentlyflashing) the turn signal 32, and is mounted in a steering column. Theturn signal lever 41 is mounted to be swingable about a support shaftwith/at a two-stage operation stroke in each of a clockwise operationdirection and a counterclockwise operation direction.

In this embodiment, the turn signal lever 41 is also used as anoperation unit operated by the driver when the driver requires theexecution of the lane change assist control. As illustrated in FIG. 4,the turn signal lever 41 is configured to be able to be operatedselectively between (i) a first stroke position P1L (P1R), which is aposition at which the turn signal lever 41 is rotated by a first angleθW1 from a neutral position PN, and (ii) a second stroke position P2L(P2R), which is a position at which the turn signal lever 41 is rotatedby a second angle θW2 (>θW1) from the neutral position PN, in each ofthe clockwise operation direction and the counterclockwise operationdirection about a support shaft O. In a state in which the turn signallever 41 is in the first stroke position P1L (P1R), when the drivercancels the lever operation (that is, the driver releases his/her handfrom the turn signal lever 41), the turn signal lever 41 isautomatically returned to the neutral position PN. In a state in whichthe turn signal lever 41 is in the second stroke position P2L (P2R),even when the driver cancels the lever operation, the turn signal lever41 is held/maintained at the second stroke position P2L (P2R) by amechanical lock mechanism (not shown). Further, in a state in which theturn signal lever 41 is held at the second stroke position P2L (P2R),when the steering wheel is reversely rotated to be returned to theneutral position, or when the driver operates the turn signal lever 41to return the turn signal lever 41 in the neutral position direction,the locking by the lock mechanism is released, and the turn signal lever41 is returned to the neutral position PN.

The turn signal lever 41 includes a first switch 411L (411R) that isturned on only when the turn signal lever 41 is tilted/rotated so as tobe at the first stroke position P1L (P1R), and a second switch 412L(412R) that turns on only when the turn signal lever 41 istilted/rotated to so as to be at the second stroke position P2L (P2R).

The steering ECU 40 detects an operation state of the turn signal lever41 based on the state of the first switch 411L (411R) and the state ofthe second switch 412L (412R). In each of the state in which turn signallever 41 is tilted to the first stroke position P1L (P1R), and the statein which the turn signal lever 41 is tilted to the second strokeposition P2L (P2R), the steering ECU 40 transmits to the meter ECU 30the turn signal flashing command including information representing theoperation direction (clockwise or counterclockwise direction) of theturn signal lever 41.

Further, when the steering ECU 40 detects that the turn signal lever 41is continuously held at the first stroke position P1L (P1R) for apredetermined set time (lane-change-request-determination time: forexample, 1 second) or more, the steering ECU 40 outputs/transmits to thedriving support ECU 10 a lane change assist request signal including theinformation representing the operation direction (clockwise orcounterclockwise direction) of the turn signal lever 41. Therefore, whenthe driver wishes to receive assistance for lane change (assistanceprovided by the lane change assist control) during driving, the drivermay tilt the turn signal lever 41 to the first stroke position P1L (P1R)in a lane change direction, and hold the turn signal lever 41 for thepredetermined set time or more. Such an operation is referred to as a“lane change assist request operation”.

In this embodiment, the turn signal lever 41 is used as the operationunit for requesting the lane change assist control. Alternatively, adedicated operation unit for requesting the lane change assist controlmay be provided in the steering wheel and the like.

The engine ECU 50 is connected to an engine actuator 51. The engineactuator 51 is an actuator for changing an operation state of aninternal combustion engine 52. In this embodiment, the internalcombustion engine 52 is a gasoline fuel injection, spark ignition,multi-cylinder engine, and includes a throttle valve for adjusting anintake air amount. The engine actuator 51 includes at least a throttlevalve actuator for changing an opening degree of the throttle valve. Theengine ECU 50 can drive the engine actuator 51, thereby changing atorque generated by the internal combustion engine 52. The torquegenerated by the internal combustion engine 52 is transmitted to drivewheels (not shown) via a transmission (not shown). Thus, the engine ECU50 can control the engine actuator 51 to control a driving force of theown vehicle, thereby changing an acceleration state (acceleration) ofthe own vehicle.

The brake ECU 60 is connected to a brake actuator 61. The brake actuator61 is provided in a hydraulic circuit between a “master cylinder (notshown) configured to pressurize a working fluid in response to astepping force on a brake pedal” and “friction brake mechanisms 62provided at the front/rear left/right wheels”. The friction brakemechanism 62 includes a brake disk 62 a fixed to the wheel and a brakecaliper 62 b fixed to the vehicle body. The brake actuator 61 isconfigured to adjust a hydraulic pressure supplied to a wheel cylinderincluded in the brake caliper 62 b in accordance with an instructionfrom the brake ECU 60 to use the hydraulic pressure to operate the wheelcylinder, thereby pressing a brake pad against the brake disk 62 a andgenerating a friction braking force. Thus, the brake ECU 60 can controlthe brake actuator 61, thereby controlling the braking force of the ownvehicle.

The navigation ECU 70 includes a GPS receiver 71 configured to receive aGPS signal for detecting a current position of the own vehicle, a mapdatabase 72 having map information and the like stored therein, and atouch panel (touch panel-type display) 73. The navigation ECU 70identifies the position of the own vehicle at the current time pointbased on the GPS signal, and performs various types of calculationprocessing based on the position of the own vehicle and the mapinformation and the like stored in the map database 72, to therebyperform route guidance with use of the touch panel 73.

The map information stored in the map database 72 includes roadinformation. The road information includes parameters (e.g., roadcurvature radius or curvature representing the degree of the curve ofthe road, the road lane width, the number of lanes of the road, and theposition of the lane center line CL of each lane) representing the shapeand the position of the road for each section of the road. Further, theroad information includes road type information for enabling distinctionof whether or not the road is a road for exclusive use by automobiles,and the like.

<Control Processing Performed by Driving Support ECU 10>

Next, control processing performed by the driving support ECU 10 isdescribed. Under a state in which both of the lane trace assist controland the adaptive cruise control are being executed, when the lane changeassist request is accepted, the driving support ECU 10 executes the lanechange assist control. In view of this, the lane trace assist controland the adaptive cruise control are first described.

<Lane Trace Assist Control (LTA)>

The lane trace assist control provides/generates the steering torqueapplied to the steering mechanism so that the position of the ownvehicle is maintained in the vicinity of the target travel line inside a“lane in which the own vehicle is traveling”, thereby assisting thesteering operation of the driver. In this embodiment, the target travelline is the lane center line CL, but a line offset/shifted in the lanewidth direction by a predetermined distance from the lane center line CLcan also be adopted as the target travel line.

In the following, the lane trace assist control is referred to as an“LTA”. The LTA is widely known (e.g., refer to Japanese PatentApplication Laid-open No. 2008-195402, Japanese Patent ApplicationLaid-open No. 2009-190464, Japanese Patent Application Laid-open No.2010-6279, and Japanese Patent No. 4349210) although the LTA itself hasvarious names. Thus, a brief description on the LTA is now given.

The driving support ECU 10 is configured to carry out the LTA when theLTA is requested through the operation applied to the setting operationunit 14. When the LTA is requested, the driving support ECU 10calculates a target steering angle θlta* in accordance with Expression(1) based on the above-mentioned lane-related vehicle information (Cu,Dy, and θy) every time a predetermined time period (calculation period)elapses.

θlta*=Klta1·Cu+Klta2·θy+Klta3·Dy+Klta4·ΣDy  (1)

In Expression (1), Klta1, Klta2, Klta3, and Klta4 are control gains. Thefirst term on the right-hand side is a steering angle component that isdetermined in accordance with the curvature Cu of the road and acts in afeed-forward manner. The second term on the right-hand side is asteering angle component that acts in the feed-back manner so that theyaw angle θy is decreased (so that the difference between the directionof the own vehicle and the lane center line CL is decreased). That is,the second term on the right-hand side is a steering angle componentcalculated by feed-back control with the target value of the yaw angleθy being set to zero. The third term on the right-hand side is asteering angle component that acts in a feed-back manner so that thelateral difference Dy, which is a positional gap (positional difference)between the own vehicle and the lane center line CL in the lane widthdirection, is decreased. That is, the third term on the right-hand sideis a steering angle component calculated by feed-back control with thetarget value of the lateral difference Dy being set to zero. The fourthterm on the right-hand side is a steering angle component that acts in afeed-back manner so that an integral value ΣDy of the lateral differenceDy is decreased. That is, the fourth term on the right-hand side is asteering angle component calculated by feed-back control with the targetvalue of the integral value ΣDy being set to zero.

A target steering angle θlta* becomes an angle to have the own vehicletravel toward the left direction, for example,

-   -   when the lane center line CL curves to the left (direction),    -   when the own vehicle is laterally shifted/deviated in the right        direction from the lane center line CL, or    -   when the own vehicle is facing/directing to the right        (direction) with respect to the lane center line CL.

Further, a target steering angle θlta* becomes an angle to have the ownvehicle travel toward the right direction,

-   -   when the lane center line CL curves to the right (direction),    -   when the own vehicle is laterally shifted/deviated in the left        direction from the lane center line CL, or    -   when the own vehicle is facing/directing to the left (direction)        with respect to the lane center line CL.

Therefore, a calculation according to the Expression (1) is made withuse of symbols (plus and minus) corresponding to the right/leftdirection.

The driving support ECU 10 outputs/transmits, to the EPS ECU 20, acommand signal including information on (representing) the targetsteering angle θlta* that is the calculation result. The EPS ECU 20controls (drives) the steering motor 22 so that the steering anglefollows (becomes equal to) the target steering angle θlta*. In thisembodiment, the driving support ECU 10 outputs/transmits the commandsignal including information on (representing) the target steering angleθlta* to the EPS ECU 20, but the driving support ECU 10 may calculate atarget torque for obtaining the target steering angle θlta*, andoutput/transmit, to the EPS ECU 20, a command signal includinginformation on (representing) the target torque that is the calculationresult. The above is the outline of the LTA.

<Adaptive Cruise Control (ACC)>

When a preceding vehicle traveling immediately ahead of the own vehicleis present, the adaptive cruise control has the own vehicle follow thepreceding vehicle while maintaining an inter-vehicle distance betweenthe preceding vehicle and the own vehicle at a predetermined distance,based on the surrounding information. When there is no precedingvehicle, the adaptive cruise control has the own vehicle travel at aconstant set vehicle speed. In the following, the adaptive cruisecontrol is referred to as an “ACC”. The ACC itself is widely known(e.g., refer to Japanese Patent Application Laid-open No. 2014-148293,Japanese Patent Application Laid-open No. 2006-315491, Japanese PatentNo. 4172434, and Japanese Patent No. 4929777). Thus, a brief descriptionon the ACC is now given.

The driving support ECU 10 is configured to carry out the ACC when theACC is requested through the operation applied to the setting operationunit 14. That is, the driving support ECU 10 is configured to select afollowing-objective-vehicle based on the surrounding informationacquired from the surrounding sensors 11 when the ACC is requested. Forexample, the driving support ECU 10 determines whether or not another-vehicle(s) is in a following-objective-vehicle area defined inadvance.

When the other-vehicle is in the following-objective-vehicle area for apredetermined time period or more, the driving support ECU 10 selectsthe other-vehicle as the following-objective-vehicle. The drivingsupport ECU 10 sets a target acceleration in such a manner that the ownvehicle follows the following-objective-vehicle. Further, when noother-vehicle is present in the following-objective-vehicle area, thedriving support ECU 10 sets the target acceleration based on a setvehicle speed and a detected vehicle speed (vehicle speed detected bythe vehicle speed sensor) in such a manner that the detected vehiclespeed of the own vehicle matches (becomes equal to) the set vehiclespeed.

The driving support ECU 10 uses the engine ECU 50 to control the engineactuator 51, and, depending on necessity, uses the brake ECU 60 tocontrol the brake actuator 61 so that the acceleration of the ownvehicle matches (becomes equal to) the target acceleration. On the otherhand, when the driver operates the accelerator pedal during the ACC, thedriving support ECU 10 prioritizes the accelerator pedal operation overthe ACC, thereby accelerating the own vehicle according to theaccelerator pedal operation.

The above is the outline of the ACC.

<Lane Change Assist Control (LCA)>

The lane change assist control will next be described. After thesurrounding of the own vehicle is monitored and it is determined thatthe own vehicle can safely change lanes, the lane change assist controlprovides/generates a steering torque to the steering mechanism so thatthe lane change assist control has the own vehicle move from the lane inwhich the own vehicle is currently traveling to the adjacent lane whilemonitoring the surrounding of the own vehicle. Thus, the driver'ssteering operation (lane change operation) is assisted. That is, thelane change assist control can have the own vehicle change lanes withoutthe driver's steering operation (steering wheel operation). In thefollowing, the lane change assist control is referred to as “LCA”.

Similarly to the LTA, the LCA is control of a lateral position of theown vehicle with respect to the lane, and is executed in place of theLTA when the lane change assist request is accepted while the LTA andthe ACC are being executed. In the following, the LTA and the LCA arecollectively referred to as “steering assist control”, and the state ofthe steering assist control is referred to as “steering assist controlstate”.

FIG. 5 illustrates a steering assist control routine executed by thedriving support ECU 10. The steering assist control routine is executedwhen a LTA execution accept condition is satisfied. The LTA executionaccept condition is satisfied when all of the following conditions andthe like are satisfied.

-   -   The execution of the LTA has been selected by use of the setting        operation unit 14.    -   The ACC is being executed.    -   The white lines have been recognized by the camera sensor 12.

As the driving support ECU 10 starts the steering assist controlroutine, at step S11, the driving support ECU 10 sets the steeringassist control state to a “LTA ON-state” to execute the LTA. The “LTAON-state” refers to the control state in which the LTA is executed.

Next, at step S12, the driving support ECU 10 determines whether or nota LCA start condition is satisfied.

For example, the LCA start condition is satisfied when all of thefollowing conditions (1) to (6) are satisfied.

1. The lane change assist request operation has been detected.2. The execution of the LCA has been selected by use of the settingoperation unit 14.3. The white line at the side on which the turn signal 32 is flashing isa broken line. That is, the white line which is the boundary between thelane (referred to as an “original lane”) in which the own vehicle iscurrently traveling and a lane adjacent to the original lane (referredto as an “adjacent lane” or a “target lane”) is a broken line.4. It is determined, based on the result of monitoring the surroundingsof the own vehicle, that the current situation around the own vehicle isa situation in which the LCA is allowed to be executed. That is, noobstacle (e.g., other vehicles, etc.) which obstructs the lane change isdetected by the surrounding sensors 11, and thus, the driving supportECU 10 has determined that the lane change can be executed safely.5. The road on the own vehicle is traveling is a road for exclusive useof automobiles. That is, the road type information acquired from thenavigation ECU 70 represents that a road on which the own vehicle istraveling is for exclusive use of automobiles.6. The vehicle speed of the own vehicle is within a predeterminedvehicle speed range for accepting the execution of the LCA.

For example, even when an other-vehicle is present in the target lane,if an inter-vehicle distance between the own vehicle and thatother-vehicle traveling in the target lane is suitably/sufficientlyensured in view of a relative speed between the own vehicle and thatother-vehicle, the above-mentioned condition 4 is satisfied.

The LCA start condition is not limited to the above-mentioned conditions1 to 6. In place of one of the conditions 1 to 6, or in addition to theconditions 1 to 6, the LCA start condition may include other conditions.

When the LCA start condition is not satisfied, the driving support ECU10 returns to step S11 and continues the execution of the LTA.

When the LCA start condition is satisfied during the execution of theLTA (S12: Yes), the driving ECU 10 executes the LCA in place of the LTA.At the start of the LCA, the driving support ECU 10 transmits to themeter ECU 30 a command for displaying start-guidance for the LCA.Therefore, the start-guidance for the LCA is displayed on the displayunit 31.

When the driving support ECU 10 starts the LCA, at step S13, the drivingsupport ECU 10 first executes a process for initializing targettrajectory calculation parameters. The target trajectory calculationparameters are used for calculation of a target trajectory. The targettrajectory for the LCA will be described below.

When executing the LCA, the driving support ECU 10 determines/specifiesa target trajectory function for defining/determining the targettrajectory of the own vehicle. The target trajectory is a trajectoryalong which the own vehicle is to be moved, for a “target lane changetime period”, from the lane (original lane) in which the own vehicle iscurrently traveling to the center position in the width direction(referred to as a “final target lateral position”) of the target lanespecified by the information included in the lane change assist requestsignal, which is adjacent to the original lane. The target trajectoryhas, for example, a shape as illustrated in FIG. 6.

As described later, the target trajectory function is a function of anelapsed time from the start of the LCA (as a variable), and forcalculating a target lateral position of the own vehicle for(corresponding to) each elapsed time with reference to the lane centerline CL of the original lane. Here, the lateral position of the ownvehicle represents the position of the center of gravity of the ownvehicle in the lane width direction (also referred to as a “lateraldirection”) with reference to the lane center line CL.

The target lane change time period is varied in proportion to a distance(hereinafter referred to as a “necessary lateral distance”) required tomove the own vehicle in the lateral direction from the initial (lateral)position at the start of the LCA to the final target lateral position.When the lane width is 3.5 m as in the case of typical roads, the targetlane change time period is set to, for example, 8.0 seconds. Thisexample corresponds to a case in which the own vehicle is positioned onthe lane center line CL of the original lane at the start of the LCA.When the lane width is, for example, 4.0 m, the target lane change timeperiod is set to 9.1 (=8.0×4.0/3.5) seconds which is a valuecorresponding to the lane width.

Further, when the lateral position of the own vehicle at the start ofthe LCA is shifted/deviated toward the target lane (i.e., to theadjacent lane side of a destination of changing lanes) with respect tothe lane center line CL of the original lane, the target lane changetime period is decreased (is made shorter) as the shift/deviation amount(magnitude of the lateral difference Dy) is increased. On the otherhand, when the lateral position of the own vehicle at the start of theLCA is shifted/deviated to a side opposite to the target lane withrespect to the lane center line CL of the original lane, the target lanechange time period is increased (is made longer) as the shift/deviationamount (magnitude of the lateral difference Dy) is increased. Forexample, when the shift/deviation amount is 0.5 m, the increase/decreaseadjustment amount of the target lane change time period may be 1.14(=8.0×0.5/3.5) seconds. The above-mentioned values for setting thetarget lane change time period are merely examples, and thus, any othervalues may be adopted.

In this embodiment, the target lateral position y is calculated inaccordance with the target trajectory function y(t) expressed byExpression (2). The target trajectory function y(t) is a fifth-orderfunction of the elapsed time t serving as a variable.

y(t)=c ₀ +c ₁ ·t+c ₂ ·t ² +c ₃ ·t ³ +c ₄ ·t ⁴ +c ₅ ·t ⁵  (2)

This target trajectory function y(t) is a function for moving the ownvehicle to the final target lateral position smoothly.

In Expression (2), the constants c₀, c₁, c₂, c₃, c₄, and c₅ aredetermined based on a state (i.e., an “initial lateral state amount” tobe described later) of the own vehicle at the start of the LCA and atarget state (i.e., a “final target lateral state amount” to bedescribed later) of the own vehicle at the completion of the LCA.

For example, as illustrated in FIG. 7, the target trajectory functiony(t) is a function for calculating the target lateral position y(t) ofthe own vehicle C corresponding to an elapsed time t (also referred toas the “present time”) from the start of the LCA (at the time of thecalculation of the target trajectory), with reference to the lane centerline CL of the lane (original lane) in which the own vehicle C iscurrently traveling. In FIG. 7, both of the original lane and the targetlane are straight. However, in a case in which both of the original laneand the target lane are curved, as illustrated in FIG. 8, the targettrajectory function y(t) can be said to be a function for calculatingthe target lateral position of the own vehicle C with respect to thecurved lane center line CL of the original lane, using the curved lanecenter line CL as the reference/standard line.

The above-mentioned target trajectory calculation parameters includeparameters for defining/determining the constants c₀, c₁, c₂, c₃, c₄,and c₅ of the target trajectory function y(t). Specifically, the targettrajectory calculation parameters include the following parameters P1 toP7.

P1: the lateral position (hereinafter referred to as an “initial lateralposition”) of the own vehicle with respect to the lane center line ofthe original lane at the start of the LCA.

P2: the speed (hereinafter referred to as an “initial lateral speed”) ofthe own vehicle in the lateral direction at the start of the LCA.

P3: the acceleration (hereinafter referred to as an “initial lateralacceleration”) of the own vehicle in the lateral direction at the startof the LCA.

P4: the target lateral position (final target lateral position) of theown vehicle with respect to the lane center line of the original lane atthe completion of the LCA.

P5: a target speed (hereinafter referred to as a “final target lateralspeed”) of the own vehicle in the lateral direction at the completion ofthe LCA.

P6: a target acceleration (hereinafter referred to as a “final targetlateral acceleration”) of the own vehicle in the lateral direction atthe completion of the LCA.

P7: the target lane change time period which is a target time periodfrom the start of the LCA to the completion of the LCA (i.e., a timelength of a period while the LCA is executed).

Further, the above-mentioned lateral direction means the width directionof the lane.

The initial lateral position is set to the same value as the lateraldifference Dy detected by the camera sensor 12 at the start of the LCA.The initial lateral speed is set to a value (v·sin(θy)) obtained bymultiplying a vehicle speed v by a sine value (sin(θy)) of the yaw angleθy. The vehicle speed v is a value detected by the vehicle speed sensorat the start of the LCA, and the yaw angle θy is a value detected by thecamera sensor 12 at the start of the LCA. Further, the initial lateralacceleration may be set to a differential value of the initial lateralspeed. However, the initial lateral acceleration may be preferably setto a value (v·γ) obtained by multiplying a yaw rate γ (rad/s) detectedby the yaw rate sensor at the start of the LCA by the vehicle speed v.This is because, in the case where the yaw rate γ (rad/s) detected bythe yaw rate sensor is used, the change in the behavior of the ownvehicle can be detected more quickly than in the case where the yawangle θy detected by the camera sensor 12 is used. The initial lateralposition, the initial lateral speed, and the initial lateralacceleration are collectively referred to as an “initial lateral stateamount (or, index, quantity)”.

In this embodiment, it is considered/regarded that the lane width of thetarget lane is the same as the lane width of the original lane detectedby the camera sensor 12 (since the lane width of the target lane is thesame as that of the original lane in most cases). Therefore, in the casewhere the own vehicle is traveling on the lane center line CL of theoriginal lane, the final target lateral position is set to the samevalue as the lane width of the original lane (the final target lateralposition=the lane width of the original lane). Further, both of thefinal target lateral speed and the final target lateral acceleration areset to zero. The final target lateral position, the final target lateralspeed, and the final target lateral acceleration are collectivelyreferred to as a “final target lateral state amount (or index,quantity)”.

As described above, the target lane change time period is calculatedbased on the lane width (which may be the lane width of the originallane) and the shift/deviation amount of the own vehicle in the lateraldirection at the start of the LCA. For example, the target lane changetime period “tlen” is calculated in accordance with Expression (3).

tlen=Dini·A  (3)

“Dini” is a necessary distance for moving the own vehicle in the lateraldirection from the position (initial lateral position) at the start ofthe LCA to the position (final target lateral position) at thecompletion of the LCA. Therefore, in the case where the own vehicle ispositioned at the lane center line CL of the original lane at the startof the LCA, “Dini” is set to the same value as the lane width. In thecase where the own vehicle is shifted/deviated from the lane center lineCL of the original lane, “Dini” is set to a value obtained by adding theshift/deviation amount to the lane width or obtained by subtracting theshift/deviation amount from the lane width. “A” is a constant which is a“target time” taken for moving the own vehicle in the lateral directionby a unit distance, and is set to 2.29 sec/m (=8 sec/3.5 m), forexample. In this case, when the “required distance Dini” for moving theown vehicle in the lateral direction is 3.5 m, the “target lane changetime period tlen” is set to 8 seconds. Hereinafter, the constant A isreferred to as a “target time constant A”.

The target time constant A is not limited to the above-mentioned value,but may be set to any value. Further, the setting operation unit 14 maybe configured in such a manner that the driver can select a value as thetarget time constant A from a plurality of values by using the settingoperation unit 14 according to the driver's preference. Alternatively,the target lane change time period may be a fixed value.

The process for initializing the target trajectory calculationparameters at step S13 is the process for setting the above-mentionedseven parameters (the initial lateral position, the initial lateralspeed, the initial lateral acceleration, the final target lateralposition, the final target lateral speed, the final target lateralacceleration, and the target lane change time period) in the mannerdescribed above.

After executing the process for initializing the target trajectorycalculation parameters at step S13, the driving support ECU 10 executesa derivation process of (for determining) the target trajectory functionat step S14. Specifically, the driving support ECU 10 calculates theconstants c₀, c₁, c₂, c₃, c₄, and c₅ of the target trajectory functiony(t) expressed by Expression (2) based on the initial lateral stateamount, the final target lateral amount, and the target lane change timeperiod, to thereby define/finalize the target trajectory function y(t).

The lateral speed y′(t) is expressed by Expression (4) based on thetarget trajectory function y(t) expressed by Expression (2). Further,the lateral acceleration y″(t) is expressed by Expression (5).

y′(t)=c ₁+2·c ₂ ·t+3·c ₃ ·t ²+4·c ₄ ·t ³+5·c ₅ ·t ⁴  (4)

y″(t)=2·c ₂+6·c ₃ ·t+12·c ₄ ·t ²+20·c ₅ ·t ³  (5)

Here, the initial lateral position is represented by “y0”, the initiallateral speed is represented by “vy0”, the initial lateral accelerationis represented by “ay0”, the final target lateral position isrepresented by “y1”, the final target lateral speed is represented by“vy1”, the final target lateral acceleration is represented by “ay1”,and the lane width of the original lane is represented by “W”. Based onthe above-mentioned target trajectory calculation parameters, thefollowing Expressions are obtained.

y(0)=c ₀ =y0  (6)

y′(0)=c ₁ =vy0  (7)

y″(0)=2·c ₂ =ay0  (8)

y(tlen)=c ₀ ·+c ₁ ·tlen+c ₂ ·tlen ² +c ₃ ·tlen ³ +c ₄ ·tlen ⁴ +c ₅ ·tlen⁵ =y1=W  (9)

y′(tlen)=c ₁+2·c ₂ ·tlen+3·c ₃ ·tlen ²+4·c ₄ ·tlen ³+5·c ₅ ·tlen ⁴=vy1=0  (10)

y″(tlen)=2·c ₂+6·c ₃ ·tlen+12·c ₄ ·tlen ²+20·c ₅ ·tlen ³ =ay1=0  (11)

Therefore, from the above Expressions (6) to (11), the constants c₀, c₁,c₂, c₃, c₄, and c₅ of the target trajectory function y(t) are obtained.Subsequently, through substituting the obtained constants c₀, c₁, c₂,c₃, c₄, and c₅ for Expression (2), the target trajectory function y(t)is derived/defined. At the same time as the derivation of the targettrajectory function y(t), the driving support ECU 10 activates a clocktimer (initial value: zero) to start counting up the elapsed time t fromthe start of the LCA.

Next, at step S15, the driving support ECU 10 calculates a targetlateral state amount of the own vehicle at the current time point. Thetarget lateral state amount includes a target lateral position which isa target value of the lateral position of the own vehicle in the lanewidth direction, a target lateral speed which is a target value of thespeed (lateral speed) of the own vehicle in the lane width direction,and a target lateral acceleration which is a target value of theacceleration (lateral acceleration) of the own vehicle in the lane widthdirection. The lateral speed and the lateral acceleration arecollectively referred to as a “lateral movement state amount”. Thetarget lateral speed and the target lateral acceleration arecollectively referred to as a “target lateral movement state amount”.

The driving support ECU 10 calculates the target lateral position at thecurrent time point, the target lateral speed at the current time point,and the target lateral acceleration at the current time point, based onthe target trajectory function y(t) derived/defined at step S14 and thepresent time “t”. The present time “t” is the elapsed time after thetarget trajectory function y(t) has been derived/defined at step S14,which is equivalent to the elapsed time from the start of the LCA, ascan be understood from processes described later. As described above,after the driving support ECU 10 derives/determines the targettrajectory function y(t) at step S14, the driving support ECU 10 resetsthe clock timer to start counting up the elapsed time “t” (=the presenttime t) from the start of the LCA. The target lateral position iscalculated through applying/assigning the present time t to the targettrajectory function y(t). The target lateral speed is calculated throughapplying/assigning the present time t to the function y′(t) obtained byfirst-order differentiating the target trajectory function y(t). Thetarget lateral acceleration is calculated through applying/assigning thepresent time t to the function y″(t) obtained by second-orderdifferentiating the target trajectory function y(t). The driving supportECU 10 reads the elapsed time t measured by the clock timer. The drivingsupport ECU 10 calculates the target lateral state amount based on themeasured elapsed time t and the above-mentioned functions.

Hereinafter, the target lateral position at the present time t isrepresented by “y*”, the target lateral speed at the present time t isrepresented by “vy*”, and the target lateral acceleration at the presenttime t is represented by “av*”. A functional unit/module of the drivingsupport ECU 10 for calculating the target lateral position y*, thetarget lateral speed vy* and the target lateral acceleration av* at stepS15 corresponds to a “target lateral state amount calculation unit” ofthe present invention.

Next, at step S16, the driving support ECU 10 calculates a target yawstate amount which is a target value relating to a movement for changingthe direction of the own vehicle (direction of the vehicle body). Thetarget yaw state amount includes a target yaw angle θy* of the ownvehicle at the present time t (current time point t), a target yaw rateγ* of the own vehicle at the present time t (current time point t), anda target curvature Cu* of the own vehicle at the present time t (currenttime point t). The target curvature Cu* is the curvature of the targettrajectory for having the own vehicle change lanes, that is, thecurvature of a curve component related to the lane change that does notinclude the curve curvature of the lane.

At step S16, the driving support ECU 10 reads the vehicle speed v at thepresent time t (current time point t) (the current vehicle speeddetected by the vehicle speed sensor). Further, the driving support ECU10 calculates the target yaw angle θy* at the present time t (currenttime point t), the target yaw rate γ* at the present time t (currenttime point t), and the target curvature Cu* at the present time t(current time point t) in accordance with Expressions (12) to (14)described below, respectively, based on the vehicle speed v, and thetarget lateral speed vy* and the target lateral acceleration ay*obtained at step S15.

θy*=sin⁻¹(vy*/v)  (12)

γ*=ay*/v  (13)

Cu*=ay*/v ²  (14)

The target yaw angle θy* is calculated through applying/assigning avalue obtained by dividing the target lateral speed vy* by the vehiclespeed v to an arc sine function. Further, the target yaw rate γ* iscalculated by dividing the target lateral acceleration ay* by thevehicle speed v. Further, the target curvature Cu* is calculated bydividing the target lateral acceleration ay* by a square value of thevehicle speed v. This functional unit/module of the driving support ECU10 for calculating the target yaw angle θy*, the target yaw rate γ*, andthe target curvature Cu* corresponds to a “target yaw state amountcalculation unit” of the present invention.

Next, at steps S17, the driving support ECU 10 calculates a targetcontrol amount for the LCA. In this embodiment, the driving support ECU10 calculates a target steering angle θlca* as the target controlamount. The target steering angle θlca* is calculated in accordance withExpression (15) described below, based on (i) the target lateralposition y* obtained at step S15, (ii) the target yaw angle θy*, thetarget yaw rate γ*, and the target curvature Cu* obtained at step S16,and (iii) the curvature Cu.

θlca*=Klca1·(Cu*+Cu)+Klca2·(θy*−θy)+Klca3·(y*−y)+Klca4·(y*−y)+Klca5·Σ(y*−y)  (15)

In Expression (15), Klta1, Klta2, Klta3, and Klta4 are control gains.“Cu” is the curvature at the present time t (current time point t) (atthe time of the calculation of θlca*), the curvature Cu being detectedby the camera sensor 12. “y” is the lateral position of the own vehicleat the present time t (current time point t) (at the time of thecalculation of θlca*), the lateral position y being detected by thecamera sensor 12, that is, corresponds to Dy. “θy” is the yaw angle ofthe own vehicle at the present time t (current time point t) (at thetime of the calculation of θlca*), the yaw angle θy being detected bythe camera sensor 12. Further, “γ” is the yaw rate of the own vehicle atthe present time t (current time point t), the yaw rate γ being detectedby the yaw rate sensor. The control gain Klta1 may be varied in responseto the vehicle speed. A differential value of the yaw angle θy may beused as the yaw rate γ.

The first term on the right-hand side of the Expression (15) is asteering angle component which is determined in accordance with a sum ofthe target curvature C* and the curvature Cu (the curve curvature of thelane) and acts in a feed-forward manner. “Klca1·Cu*” is a feed-forwardcontrol amount for having the own vehicle change lanes, and “Klca1·Cu”is a feed-forward control amount for having the own vehicle travel alonga curved lane with the curvature Cu. The second term on the right-handside of the Expression (15) is a steering angle component that acts inthe feed-back manner so that the deference between the target yaw angleθy* and the actual yaw angle θy is decreased. The third term on theright-hand side of the Expression (15) is a steering angle componentthat acts in a feed-back manner so that the difference between thetarget lateral position y* and the actual lateral position y isdecreased. The fourth term on the right-hand side of the Expression (15)is a steering angle component that acts in a feed-back manner so thatthe difference between the target yaw rate γ* and the actual yaw rate γis decreased. The fifth term on the right-hand side of the Expression(15) is a steering angle component that acts in a feed-back manner sothat an integral value Σ(y*−y) of the difference between the targetlateral position y* and the actual lateral position y is decreased.Therefore, the first term on the right-hand side of the Expression (15)represents the feed-forward control amount, and the second to fifthterms on the right-hand side of the Expression (15) represent thefeed-back control amount(s).

The calculation method of the target steering angle θlca* is not limitedto the above-mentioned method where the target steering angle θlca* iscalculated by using the above-mentioned five steering angle components.The target steering angle θlca* may be calculated by using at least onesteering angle component among the above-mentioned five steering anglecomponents, or may be calculated by using any other steering anglecomponent(s) in addition to the above-mentioned five steering anglecomponents or in place of at least one of the above-mentioned fivesteering angle components. As the feed-back control amount relating tothe yaw movement, either one of the “deference between the target yawangle θy* and the actual yaw angle θy” and the “difference between thetarget yaw rate γ* and the actual yaw rate γ” may be used. Further, thefeed-back control amount using the integral value Σ(y*−y) of thedifference between the target lateral position y* and the actual lateralposition y may be omitted.

After calculating the target control amount at step S17, at the nextstep S18, the driving support ECU 10 transmits a steering commandincluding information on (representing) the target control amount to theEPS ECU 20. In this embodiment, the driving support ECU 10 calculatesthe target steering angle θlca* as the target control amount. However,the driving support ECU 10 may calculate a target torque correspondingto the target steering angle θlca* and transmit a steering commandincluding information on (representing) the target torque to the EPS ECU20.

When the EPS ECU 20 receives the steering command transmitted from thedriving support ECU 10 via the CAN 100, the EPS ECU 20 drives (controls)the steering motor 22 in such a manner that the steering angle follows(becomes equal to) the target steering angle θlca*.

Next, at step S19, the driving support ECU 10 determines/confirmswhether or not the driver has performed the steering operation in thelane change direction (that is, the driver has operated/rotated thesteering wheel in a direction corresponding to the lane changedirection). For example, when the lane change in the right direction isbeing executed through the LCA, the driving support ECU 10 determineswhether or not the driver has operated/rotated the steering wheel in theright direction (clockwise direction). On other hand, when the lanechange in the left direction is being executed through the LCA, thedriving support ECU 10 determines whether or not the driver hasoperated/rotated the steering wheel in the left direction(counterclockwise direction). At step 19, the driving support ECU 10determines that the driver has performed the steering operation, onlywhen the driver has terminated the steering operation after the driverstarted that operation. Therefore, at step S19, the driving support ECU10 makes a “Yes” determination at the time point when one steeringoperation (a single consecutive steering operation) has been terminated.

When the driving support ECU 10 determines that the driver has notperformed the steering operation in the lane change direction, thedriving support ECU 10 makes a “No” determination at step S19, and thenproceeds the process to step S20.

At step S20, the driving support ECU 10 determines whether or not a LCAcompletion condition is satisfied. In this embodiment, the LCAcompletion condition is satisfied when the lateral position y of the ownvehicle reaches the final target lateral position y*. When the LCAcompletion condition is not satisfied (S20:No), the driving support ECU10 returns the process to step S15, and repeats the above-mentionedprocesses. Therefore, the driving support ECU 10 repeats the processesof steps S15 to S20 every time the predetermined time period elapses.Therefore, the target lateral state amount (y*, vy*, and ay*) iscalculated in response to the elapsed time t, and then, the target yawstate amount (θy*, y*, and Cu*) is calculated based on the calculatedtarget lateral state amount (y*, vy*, and ay*). Further, the targetcontrol amount (θlca*) is calculated based on the calculated target yawstate amount (θy*, y*, and Cu*).

Every time the driving support ECU 10 calculates/updates the targetcontrol amount (θlca*), the driving support ECU 10 transmits thesteering command including the information on (representing) the targetcontrol amount (θlca*) to the EPS ECU 20. In this manner, the drivingsupport ECU 10 can have the own vehicle travel along (according to) thetarget trajectory.

When the driving support ECU 10 determines that the LCA completioncondition is satisfied at step S20, the driving support ECU 10 sets thesteering assist control state to the LTA ON-state at step S21. That is,the driving support ECU 10 terminates/ends the LCA and resumes the LTA.Therefore, the steering assist control (LTA) is performed in such amanner that the own vehicle travels along (according to) the lane centerline CL of the target lane.

The driving support ECU 10 receives from the camera sensor 12 thelane-related vehicle information (Cu, Dy, and θy) relating to the lanein which the own vehicle is currently traveling. When the travelingposition of the own vehicle is switched from the original lane to thetarget lane, the lane-related vehicle information (Cu, Dy, and θy) to betransmitted from the camera sensor 12 to the driving support ECU 10 isswitched from the lane-related vehicle information (Cu, Dy, and θy)associated with the original lane to the lane-related vehicleinformation (Cu, Dy, and θy) associated with the target lane. Therefore,when the traveling position of the own vehicle is switched from theoriginal lane to the target lane, the sign (plus or minus) of thelateral difference Dy is reversed. When the driving support ECU 10 hasdetected the change in the sign of the lateral difference Dy transmittedfrom the camera sensor 12, the driving support ECU 10 shifts the targettrajectory function y(t) expressed by Expression (2) by the lane widthW. Specifically, the driving support ECU 10 converts the targettrajectory function y(t) expressed by Expression (2) into a targettrajectory function y(t) expressed by Expressions (2A) or (2B) describedbelow depending on the lane change direction, by substantially shiftingthe target trajectory function y(t) expressed by Expression (2) by thelane width W. Therefore, the apparatus according to the presentembodiment can convert “the target trajectory function calculated basedon the lane center line of the original lane which serves as the origin”into “the target trajectory function based on the lane center line ofthe target lane which serves as the origin”.

y(t)=W−|c ₀ +c ₁ ·t+c ₂ ·t ² +c ₃ ·t ³ +c ₄ ·t ⁴ +c ₅ ·t ⁵|  (2A)

y(t)=−(W−|c ₀ +c ₁ ·t+c ₂ ·t ² +c ₃ ·t ³ +c ⁴ ·t ⁴ +c ₅ ·t ⁵|)  (2B)

When the driving support ECU 10 determines that the driver has performedthe steering operation in the lane change direction during the executionof the LCA, the driving support ECU 10 makes a “Yes” determination atstep S19, and then, proceeds the process to step S22.

The process at step 19 for determining the steering operation performedby the driver will be described more specifically below. The drivingsupport ECU 10 executes a steering operation determination routineillustrated in FIG. 9 in parallel with the steering assist controlroutine. The driving support ECU 10 executes the steering operationdetermination routine every time a predetermined time period elapses. Atstep S191, the driving support ECU 10 first determines/confirms whetheror not a steering start flag F is zero.

When the steering start flag F is zero, at step S192, the drivingsupport ECU 10 determines whether or not the steering torque Tr detectedby the steering torque sensor is equal to or higher than a firstthreshold Tr1. This first threshold Tr1 is a threshold for determiningthe start of the steering operation performed by the driver in the lanechange direction. When the steering torque Tr is a torque in theopposite direction to the lane change direction, the driving support ECU10 always makes a “No” determination at step S192. Further, when thesteering torque Tr is compared (at step S191) with the first threshold,the absolute value of the steering torque Tr is used.

When the steering torque Tr is lower than the first threshold Tr1(S192:No), the driving support ECU 10 tentatively terminates thesteering operation determination routine. The driving support ECU 10executes the steering operation determination routine every time thepredetermined time period elapses. When the steering torque Tr becomesequal to or higher than the first threshold Tr1 (S192:Yes) while thesteering operation determination routine is repeated, the drivingsupport ECU 10 determines that the driver has started the steeringoperation in the lane change direction. Next, at step S193, the drivingsupport ECU 10 sets the steering start flag F to “1” (F<−1), and then,tentatively terminates the steering operation determination routine.

When the driving support ECU 10 resumes the steering operationdetermination routine after setting the steering start flag F to “1”,the driving support ECU 10 makes a “No” determination at step S191. Inthis case, at step S194, the driving support ECU 10 determines whetheror not the steering torque Tr detected by the steering torque sensor isequal to or lower than a second threshold Tr2. This second threshold Tr2is a threshold for determining the termination of the steering operationin the lane change direction performed by the driver. The secondthreshold Tr2 is lower than the first threshold Tr1.

When the steering torque Tr has not decreased to the second thresholdTr2 or lower (S194: No), the driving support ECU 10 tentativelyterminates the steering operation determination routine. The drivingsupport ECU 10 executes the above-mentioned processes every time thepredetermined time period elapses. When the steering torque Tr hasdecreased to the second threshold Tr2 or lower (S194:Yes) while thesteering operation determination routine is repeated, the drivingsupport ECU 10 determines that the driver has terminated the steeringoperation in the lane change direction. Next, at step S195, the drivingsupport ECU 10 determines that the driver has performed the steeringoperation in the lane change direction.

When the driving support ECU 10 determines that the driver has performedthe steering operation in the lane change direction at step S195, thedriving support ECU 10 resets the steering start flag F (F<−0) at stepS196, and then, tentatively terminates the steering operationdetermination routine.

After the driving support ECU 10 determines that the driver hasperformed the steering operation in the lane change direction at stepS195, the driving support ECU 10 makes a “Yes” determination at step S19in the steering assist control routine. According to this routine fordetermining the steering operation, the determination can easily be madeas to whether the driver has performed the steering operation.

In addition, a case is considered where the LCA is started while thedriver is performing the steering operation (for example, the vehicle istraveling on a curved lane). In this case, when the driving support ECU10 determines that the driver has terminated the steering operation(that is, the steering torque Tr has decreased to the second thresholdTr2 or lower) after the start of the LCA, the driving support ECU 10determines that the driver has performed the steering operation.Therefore, for determining that the driver has performed the steeringoperation, the driving support ECU 10 does not necessarily have todetect the start of the steering operation by the driver after the startof the LCA. The driving support ECU 10 may detect at least thetermination of the steering operation during the execution of the LCA.

The steering assist control routine (FIG. 5) will be again describedbelow. When the driving support ECU 10 determines that the driver hasperformed the steering operation (S19:Yes), at step S22, the drivingsupport ECU 10 reinitializes the target trajectory calculationparameters. At this step S22, the driving support ECU 10 recalculatesthe target trajectory calculation parameters at the present time (timeat which it is determined that the driver has performed the steeringoperation: this is also referred to as a “steering determination timepoint tst”). The target trajectory calculation parameters include thefollowing seven parameters (P11 to P17).

P11: the lateral position (hereinafter referred to as a “lateralposition yst”) of the own vehicle with respect to the lane center lineat the steering determination time point tst.

P12: the speed (hereinafter referred to as a “lateral speed vyst”) ofthe own vehicle in the lateral direction at the steering determinationtime point tst.

P13: the acceleration (hereinafter referred to as a “lateralacceleration ayst”) of the own vehicle in the lateral direction at thesteering determination time point tst.

P14: the target lateral position (final target lateral position) of theown vehicle with respect to the lane center line at the completion ofthe LCA.

P15: the target speed (final target lateral speed) of the own vehicle inthe lateral direction at the completion of the LCA.

P16: the target acceleration (final target lateral acceleration) of theown vehicle in the lateral direction at the completion of the LCA.

P17: the target lane change time period which is modified based on atarget remaining time period to the completion of the LCA (hereinafterreferred to as a “target lane change remaining time period trest*”).

Regarding the lateral position yst which is the target trajectorycalculation parameter P11, the lateral speed vyst which is the targettrajectory calculation parameter P12, and the lateral acceleration aystwhich is the target trajectory calculation parameter P13, actualdetection values of those parameters are used, respectively. Forexample, the lateral position yst which is the target trajectorycalculation parameter P11 is set to the same value as the lateraldifference Dy1 detected by the camera sensor 12 at the steeringdetermination time point tst. The lateral speed vyst which is the targettrajectory calculation parameter P12 is set to a value (v1·sin(θy1))obtained by multiplying a vehicle speed v1 by a sine value (sin(θy1)) ofa yaw angle θy1. Here, the vehicle speed v1 is a value detected by thevehicle speed sensor at the steering determination time point tst, andthe yaw angle θy1 is a value detected by the camera sensor 12 at thesteering determination time point tst. Further, the lateral accelerationayst which is the target trajectory calculation parameter P13 may be setto a differential value of the lateral speed vyst. However, the lateralacceleration ayst may be preferably set to a value (v1·γ1) obtained bymultiplying a yaw rate γ1 (rad/s) detected by the yaw rate sensor at thesteering determination time point tst by the vehicle speed v1.

In a case where the own vehicle is present in the original lane, thelateral difference Dy1 and the yaw angle θy1 are detected on the basisof (with respect to) the lane center line CL of the original lane. Onthe other hand, in a case where the own vehicle is present in the targetlane, the lateral difference Dy1 and the yaw angle θy1 are detected onthe basis of (with respect to) the lane center line CL of the targetlane.

Hereinafter, the lateral speed vyst and the lateral acceleration aystare collectively referred to as a “lateral movement state amount Mst” atthe steering determination time point tst. The lateral position yst andthe lateral movement state amount Mst are collectively referred to as a“lateral state amount Mkst” at the steering determination time pointtst.

The final target lateral position which is the target trajectorycalculation parameter P14 is set to a position on the lane center lineCL of the target lane. Further, both the final target lateral speedwhich is the target trajectory calculation parameter P15 and the finaltarget lateral acceleration which is the target trajectory calculationparameter P16 are set to zero.

The target lane change remaining time period trest* which is related tothe target trajectory calculation parameter P17 is calculated based onthe target time constant A, and a remaining distance (referred to as“Drest”) at the steering determination time point tst which is adistance required for having the own vehicle move in the lane widthdirection to (until) the completion of the LCA. The remaining distanceDrest represents a distance in the lane width direction from (between)the lateral position yst specified by the lateral difference Dy detectedby the camera sensor 12 at the steering determination time point tst to(and) the final target lateral position.

The target lane change remaining time period trest* is calculated inaccordance with Expression (16).

trest*=Drest·A  (16)

The driving support ECU 10 modifies/corrects the target lane change timeperiod tlen based on the steering determination time point tst and thetarget lane change remaining time period trest*. Here, it is assumedthat an elapse time from the start of the LCA (t=0) to the steeringdetermination time point tst is “tst”. Therefore, the target lane changetime period tlen is again calculated and set according to Expression(17).

tlen=tst+trest*  (17)

The driving support ECU 10 reinitializes the target trajectorycalculation parameter at step S22, and then, the driving support ECU 10determines again (recalculates) the target trajectory function at stepS23. Specifically, the driving support ECU 10 calculates the constantsc₀, c₁, c₂, c₃, c₄, and c₅ of the target trajectory function y(t)expressed by Expression (2) based on the lateral state amount Mkst atthe steering determination time point tst, the final target lateralstate amount, and the target lane change time period tlen, which are setat step S22. In such a way, the driving support ECU 10 again defines thetarget trajectory function y(t).

For example, the constants c₀, c₁, c₂, c₃, c₄, and c₅ can be calculatedin accordance with the following conditions for reinitializing thetarget trajectory calculation parameters:

y(tst)=yst

y′(tst)=vyst

y″(tst)=ayst

y(tlen)=W

y′(tlen)=0

y″(tlen)=0

Consequently, the target trajectory function f(t) can be set/determined,which enables a state of the own vehicle to be transit/vary smoothlyfrom the lateral state at the steering determination time point tst tothe final target lateral state.

If the own vehicle is present in the target lane at the steeringdetermination time point tst, the target trajectory function y(t) ismodified/converted in such a manner that the lane center line CL of thetarget lane is the origin. The lateral difference Dy with respect to thelane center line CL of the target lane is used as the lateral positionyst at the steering determination time point tst. Therefore, y(tlen) isset to be equal to “0” in place of “W” (that is, y(tlen)=0).

After the driving support ECU 10 has completed the recalculation of thetarget trajectory function y(t), the driving support ECU 10 proceeds theprocess to step S15, and repeats the above-mentioned processes. In thismanner, the vehicle can travel along the newly generated targettrajectory (that is, the recalculated target trajectory).

When the driving support ECU 10 determines that the LCA completioncondition is satisfied at step S20, the driving support ECU 10 sets thesteering assist control state to the LTA ON-state at step S21. That is,the driving support ECU 10 terminates/ends the LCA and resumes the LTA.Therefore, the steering assist control (LTA) starts to be performed insuch a manner that the own vehicle travels along (according to) the lanecenter line CL of the target lane. After the driving support ECU 10 setsthe steering assist control state to the LTA ON-state, the drivingsupport ECU 10 proceeds the process to step S11, and repeats theabove-mentioned processes.

Further, during a period in which the driving support ECU 10 isexecuting the LCA, the driving support ECU 10 continues transmitting, tothe meter ECU 30, a flashing command to intermittently flash the turnsignal 32 (at the side) corresponding to the operation direction of theturn signal lever 41. The turn signal 32 starts to beintermittently-flashed before the LCA is started, in response to theflashing command which starts to be transmitted from the steering ECU 40when the turn signal lever 41 is operated to be positioned at the firststroke position P1L (P1R). Even when and after the steering ECU 40 stopstransmitting the flashing command, the turn signal 32 continuesintermittently-flashing in response to the flashing command transmittedfrom the driving support ECU 10. In this case, a time point at whichintermittently-flashing of the turn signal 32 is terminated may be thesame as the timepoint of the completion of the LCA or before thecompletion of the LCA. For example, the intermittently-flashing of theturn signal 32 may be terminated when the own vehicle reaches a lateralposition which is away (in the original lane side) from the final targetlateral position by a predetermined extinguishment permission distance(for example, 50 cm).

According to the above-described lane change assist apparatus, when theLCA is started, the target trajectory function is calculated (determinedthrough the calculation), and then, the steering angle is controlled insuch a manner that the own vehicle travels along the target trajectoryset/determined by use of the calculated target trajectory function (thatis, the lateral state of the own vehicle matches (becomes equal to) thetarget lateral state in accordance with the elapsed time from the startof the LCA). When it is determined that the driver has performed thesteering operation in the lane change direction during the LCA, thetarget trajectory function is recalculated (determined again through therecalculation) based on the lateral state amount at that time point(i.e., the lateral state amount Mkst at the steering determination timepoint tst). This enables the target trajectory function to becalculated/determined suitably in response to the behavior of the ownvehicle which is being changed by the steering operation performed bythe driver. Based on the suitably-calculated target trajectory function,the steering of the right and left steered wheels is controlled.Accordingly, the own vehicle can change lanes in accordance with thetarget trajectory reflecting (along with) the intention of the driver'ssteering operation.

Further, when the target trajectory function is recalculated, the targetlane change remaining time period trest* is set based on the remainingdistance Drest which is a distance required to complete the LCA. Thetarget lane change time period tlen is modified/corrected based on thetarget lane change remaining time period trest*. This enables the ownvehicle to change lanes in accordance with the target trajectoryreflecting the intention of the driver's steering operation moreeffectively.

Further, in the present embodiment, when executing the LCA, the drivingsupport ECU 10 calculates the target trajectory function y(t) based onthe initial lateral position, the initial lateral speed, the initiallateral acceleration, the final target lateral position, the finaltarget lateral speed, the final target lateral acceleration, and thetarget lane change time period. While the LCA is being executed, thedriving support ECU 10 successively (sequentially) calculates the targetlateral position y*, the target lateral speed vy*, and the targetlateral acceleration ay* in accordance with the elapsed time t from thestart of the LCA (for each elapsed time t). Further, the driving supportECU 10 successively (sequentially) acquires the vehicle speed v at thecurrent time point (present time) t. The driving support ECU 10successively (sequentially) calculates the target yaw angle θy*, thetarget yaw rate γ*, and the target curvature Cu* which are target valuesrelating to the movement for changing the direction of the own vehicle,based on the acquired vehicle speed v, the target lateral speed vy*, andthe target lateral acceleration ay*. The driving support ECU 10 controlsthe steering of right and left steered wheels based on the targetlateral position y*, the target yaw angle θy*, the target yaw rate γ*,and the target curvature Cu*. Therefore, the lane change assistapparatus according to the present embodiment can have the own vehiclechange lanes smoothly according to the target trajectory function.Further, since the target yaw state amount is set in response to thevehicle speed, the own vehicle can be made to change lanes in a smoothmanner while reflecting the accelerator pedal operation performed by thedriver (i.e., change in the vehicle speed). Further, smooth lane changecan be performed in cooperation with acceleration/deceleration controlby the ACC.

Further, the target lateral speed (final target lateral speed) of theown vehicle at the completion of the LCA and the target lateralacceleration (final target lateral acceleration) of the own vehicle atthe completion of the LCA are both set to zero. In addition, the targetlateral position (final target lateral position) of the own vehicle atthe completion of the LCA is set to the center position of the targetlane in the lane width direction. Therefore, after the completion of theLCA, the driving support ECU 10 can have the own vehicle travel along(according to) the lane center line CL of the target lane with the LTA.Accordingly, the steering assist control can be smoothly switched fromthe LCA to the LTA.

Modified Example 1 for Recalculation of Target Trajectory Function

In the above-described steering assist control routine (FIG. 5), thetarget trajectory function is recalculated (steps S22 and S23) everytime it is determined that the driver has performed the steeringoperation. If the target trajectory function is frequently recalculated,the behavior of the own vehicle may be unstable. In addition, thesteering torque sensor may detect the steering torque even in asituation where the steering operation by the driver has not beenperformed, due to a disturbance torque input from the road surface, etc.In order to solve the above problem, in this modified example 1, oncethe target trajectory function is recalculated (steps S22 and S23), thetarget trajectory function is not recalculated thereafter. For example,as illustrated in FIG. 10, in the steering assist control routine (FIG.5) of the embodiment, the process of step S30 is preferably addedbetween step S19 and step S22. FIG. 10 illustrates mainly a modifiedportion in the steering assist control routine according to the modifiedexample 1.

When the driving support ECU 10 determines that the driver has performedthe steering operation (S19:Yes), the driving support ECU 10 proceedsthe process to step S30. At step S30, the driving support ECU 10determines that recalculation of the target trajectory function (S23)has been already performed after the start of the LCA. Whenrecalculation of the target trajectory function (S23) has never beenperformed, the driving support ECU 10 makes a “No” determination at stepS30, and then, proceeds the process to step S22. On the other hand, whenrecalculation of the target trajectory function (S23) has been alreadyperformed, the driving support ECU 10 makes a “Yes” determination atstep S30, and then, proceeds the process to step S20.

According to the steering assist control routine in this modifiedexample 1, the number of times of recalculation of the target trajectoryfunction is limited to once. Therefore, the own vehicle can be made tochange lanes more stably.

Modified Example 2 for Recalculation of Target Trajectory Function

When the driver has performed the steering operation during theexecution of the LCA, if the actual lateral position of the own vehicledoes not greatly deviate from the target lateral position in the lanechange direction, the target trajectory function calculated at the startof the LCA may be used as it is (it may be continued being used). Thus,in this modified example 2, only when a deviation between the actuallateral position of the own vehicle and the target lateral positioncalculated from the target trajectory function is equal to or higherthan a predetermined threshold and the actual lateral position ispositioned at a position deviated/shifted in the lane change directionwith respect to the target lateral position, the driving support ECU 10executes recalculation of the target trajectory function (steps S22 andS23).

For example, as illustrated in FIG. 11, in the steering assist controlroutine (FIG. 5) of the embodiment, steps S31 to S33 are preferablyadded between step S19 and step S22. FIG. 11 illustrates mainly amodified portion in the steering assist control routine according to themodified example 2.

When the driving support ECU 10 determines that the driver has performedthe steering operation (S19: Yes), the driving support ECU 10 proceedsthe process to step S31. At step S31, the driving support ECU 10determines whether or not the actual lateral position at the currenttime point is positioned at a position deviated/shifted in the lanechange direction with respect to the target lateral position (i.e.,whether or not the actual lateral position at the current time point ispositioned in the lane change direction side of the target lateralposition). The actual lateral position is the lateral position yst atthe steering determination time point tst, and the target lateralposition is the value y(tst) obtained by substituting the steeringdetermination time point tst into the target trajectory function y(t).When the actual lateral position at the current time point is notdeviated/shifted with respect to the target lateral position (S31: No),the driving support ECU 10 proceeds the process to step S20. On theother hand, when the actual lateral position at the current time pointis positioned at a position deviated/shifted in the lane changedirection with respect to the target lateral position (S31: Yes), thedriving support ECU 10 proceeds the process to step S32. At step 32, thedriving support ECU 10 calculates a deviation Δy (=|y(tst)−yst|) betweenthe target lateral position y(tst) and the actual lateral position yst.Next, at step S33, the driving support ECU 10 determines whether or notthe deviation Δy is equal to or larger than a predetermined thresholdΔyref. This threshold Δyref is a threshold for determining whether ornot it is necessary to recalculate the target trajectory function.

When the deviation Δy is smaller than the threshold Δyref (S33: No),because it is not necessary to recalculate the target trajectoryfunction, the driving support ECU 10 proceeds the process to step S20.On the other hand, when the deviation Δy is equal to or higher than thethreshold Δyref (S33:Yes), the driving support ECU 10 proceeds theprocess to step S22.

According to the steering assist control routine of the modified example2, the target trajectory function is not calculated more than necessary.Therefore, the apparatus according to the modified example 2 can havethe own vehicle change lanes more stably. In addition, the calculationload of the microcomputer of the driving support ECU 10 can be reduced.

The processes of the modified example 2 may be incorporated into theroutine in the modified example 1. In this configuration, steps S31 toS33 are added between step S30 and step S22 in the routine of FIG. 10.

<Modified Calculation Example of Target Lane Change Remaining TimePeriod>

In the above-described embodiment, the target lane change remaining timeperiod trest* is calculated by multiplying the remaining distance Drestby the target time constant A in accordance with Expression (16). Inthis modified example, the driving support ECU 10 modifies/corrects thetarget lane change remaining time period trest* by using the actuallateral speed vyst at the steering determination time point tst. Forexample, the remaining distance Drest is corrected so as to be madeshorter by using the actual lateral speed vyst in accordance withExpression (18). This enables the target lane change remaining timetrest* to be adjusted so that the time trest* becomes shorter.

Drest1=Drest−α×vyst  (18)

Drest1 is a modified remaining distance. Further, a is a predeterminedreduction coefficient and is set to a small positive value. The actuallateral speed vyst is defined to have a positive value when the actuallateral speed vyst is speed in the same direction as the lane changedirection. The remaining distance Drest of Expression (16) is replacedwith the modified remaining distance Drest1 (Drest<−Drest1).Consequently, the target lane change remaining time trest* is correctedto become shorter, as the actual lateral speed vyst in the lane changedirection at the steering determination time point is higher.

Further, the target lane change remaining time trest* may be limitedwith a predetermined lower limit guard value so that the target lanechange remaining time trest* does not become shorter than thepredetermined lower limit value.

Further, the target lane change remaining time trest* may be correctedby using the actual lateral acceleration ayst at the steeringdetermination time point tst. In this configuration, the modifiedremaining distance Drest1 may be calculated in accordance withExpression (19).

Drest1=Drest−β×ayst  (19)

β is a predetermined reduction coefficient and is set to a smallpositive value. The actual lateral acceleration ayst is defined to havea positive value when the actual lateral acceleration ayst isacceleration in the same direction as the lane change direction.

Further, the target lane change remaining time trest* may be correctedby using both the actual lateral speed vyst at the steeringdetermination time point tst and the actual lateral acceleration ayst atthe steering determination time point tst. In this configuration, themodified remaining distance Drest1 may be calculated in accordance withExpression (20).

Drest1=Drest−(α×vyst+β×ayst)  (20)

According to the above-mentioned examples, as “the actual lateral speedvyst and/or the actual lateral acceleration ayst” in the lane changedirection at the steering determination time point is larger, the targetlane change remaining time trest* is corrected/modified so as to beshorter. Therefore, the target trajectory function can becalculated/determined in a more suitable manner. Accordingly, the ownvehicle can be made to change lanes in accordance with the targettrajectory reflecting the intention of the driver's steering operationmore effectively.

In the above, the lane change assist apparatus according to theembodiment has been described, but the present invention is not limitedto the above-mentioned embodiment, and various changes are possiblewithin the range not departing from the object of the present invention.

For example, in the above-described embodiment, the determination ismade as to whether or not the driver has performed the steeringoperation only when the steering operation is an operation which has theown vehicle move in the lane changing direction. However, there is nonecessity to do so, and the presence or absence of the steeringoperation performed by the driver may be determined regardless of theoperation direction of the steering wheel. For example, during the LCA,the driver may find an obstacle present on the road surface and performthe steering wheel in the opposite direction to the lane changedirection so as to avoid the obstacle. Even in such a case,recalculation of the target trajectory function may be effectivelyperformed.

Further, in the above-described embodiment, the target lane change timeperiod tlen is changed in accordance with the remaining distance Drest.However, there is no necessity to do so. A configuration may be adoptedin which the target lane change time period tlen is not changed (or keptunchanged) during the LCA.

In the above-described embodiment, the target trajectory calculationparameters P11, P12 and P13 set at the steering determination time pointtst are actual detected values. Alternatively, those parameters may becalculated in consideration of the target lateral state amountcalculated at the steering determination time point tst, that is, atleast one of the target lateral position, the target lateral speed, andthe target lateral acceleration. For example, the lateral position ystat the steering determination time point tst may be set/determined basedon both “the target lateral position and the actual lateral position” atthe steering determination time point tst, such as by obtaining aweighted average value between “the target lateral position and theactual lateral position” at the steering determination time point tst,using a predetermined weighting ratio. Similarly, the lateral speed vystat the steering determination time point tst may be set/determined basedon both “the target lateral speed and the actual lateral speed” at thesteering determination time point tst, such as by obtaining a weightedaverage value between “the target lateral speed and the actual lateralspeed” at the steering determination time point tst, using apredetermined weighting ratio. Furthermore, the lateral accelerationayst at the steering determination time point tst may be set/determinedbased on both “the target lateral acceleration and the actual lateralacceleration” at the steering determination time point tst, such as byobtaining a weighted average value between “the target lateralacceleration and the actual lateral acceleration” at the steeringdetermination time point tst, using a predetermined weighting ratio.

In the above-described embodiment, a fifth-order function is used as thetarget trajectory function. However, it is not always necessary to use afifth-order function. In the above-described embodiment, the targetlateral speed and the target lateral acceleration are calculated to tobe used as the target lateral movement state amount. However, only thetarget lateral speed or only the target lateral acceleration may becalculated to be used as the target lateral movement state amount. Inthe above-described embodiment, the target yaw angle, the target yawrate, and the target curvature are calculated to be used as the targetyaw state amount. However, at least one of them may be calculated to beused as the target yaw state amount.

For example, in the above embodiment, it is a prerequisite for carryingout the LCA that the steering assist control state is in the LTAON-state (that is, the LTA is being executed). In other words, the LCAdoes not start to be executed unless the steering assist control stateis in the LTA ON-state. However, such a prerequisite is not necessarilyrequired to start the LCA. Further, as a prerequisite for carrying outthe LCA, there is no need to assume that the ACC is being executed. Inother words, the LCA may be able to be started even if the steeringassist control state is not in the LTA ON-state. In the aboveembodiment, the LCA start condition includes the following condition:the road on which the own vehicle is traveling is a road for exclusiveuse of automobiles. However, the LCA start condition does notnecessarily include such a condition.

What is claimed is:
 1. A lane change assist apparatus for vehiclecomprising: a lane recognition unit for recognizing a lane to detect arelative positional relationship of an own vehicle with respect to thelane; a target trajectory calculation unit for, based on the relativepositional relationship of the own vehicle with respect to the lane,calculating a target trajectory for having the own vehicle change lanestoward an adjacent lane; and an assist control unit for performing alane change assist control to control steering of a steered wheel insuch a manner that the own vehicle travels along the target trajectory,wherein the lane change assist apparatus further comprises a steeringoperation determination unit for determining whether or not a driver hasperformed a steering operation while the lane change assist control isbeing performed, wherein the target trajectory calculation unitcomprises: a first calculation unit for, at a start of the lane changeassist control, calculating the target trajectory along which the ownvehicle is to travel from the start of the lane change assist controluntil a completion of the lane change assist control; and a secondcalculation unit for, at a steering determination time point at whichthe steering operation determination unit determines that the driver hasperformed the steering operation, calculating the target trajectoryalong which the own vehicle is to travel from the steering determinationtime point until the completion of the lane change assist control, basedon a lateral position which is a position of the own vehicle in a lanewidth direction at the steering determination time point, and a lateralmovement state amount representing a movement state of the own vehiclein the lane width direction at the steering determination time point,and wherein, the assist control unit is configured to: control thesteering of the steered wheel in such a manner that the own vehicletravels along the target trajectory calculated by the first calculationunit until the steering determination time point; and control thesteering of the steered wheel in such a manner that the own vehicletravels along the target trajectory calculated by the second calculationunit after the steering determination time point.
 2. The lane changeassist apparatus according to claim 1, wherein, the first calculationunit is configured to calculate, as the target trajectory, a targettrajectory function representing a target lateral position which is atarget position of the own vehicle in the lane width direction inaccordance with a first elapse time from the start of the lane changeassist control, until the completion of the lane change assist control,and the second calculation unit is configured to calculate, as thetarget trajectory, a target trajectory function representing a targetlateral position which is a target position of the own vehicle in thelane width direction in accordance with a second elapse time from thesteering determination time point, until the completion of the lanechange assist control.
 3. The lane change assist apparatus according toclaim 2, wherein the assist control unit comprises: a target lateralstate amount calculation unit for, based on the target trajectoryfunction calculated by the first calculation unit or the secondcalculation unit, successively calculating a target lateral state amountwhich represents a target lateral position of the own vehicle at acurrent time point and a target lateral movement state amount, thetarget lateral movement state amount being a target value of a movementstate of the own vehicle in the lane width direction at the current timepoint; a target yaw state amount calculation unit for successivelyacquiring a vehicle speed of the own vehicle at the current time point,and successively calculating a target yaw state amount which is a targetvalue at the current time point related to a movement for changing adirection of the own vehicle, based on the vehicle speed and the targetlateral movement state amount; and a steering control unit forcontrolling the steering of the steered wheel based on the targetlateral position and the target yaw state amount.
 4. The lane changeassist apparatus according to claim 2, wherein the first calculationunit is configured to calculate the target trajectory functionrepresenting the target lateral position which is the target position ofthe own vehicle in the lane width direction in accordance with the firstelapse time from the start of the lane change assist control, based on:(i) an initial lateral state amount representing a lateral position ofthe own vehicle at the start of the lane change assist control and alateral movement state amount which is a movement state of the ownvehicle in the lane width direction at the start of the lane changeassist control; (ii) a final target lateral state amount representing atarget lateral position of the own vehicle at the completion of the lanechange assist control and a target lateral movement state amount of theown vehicle at the completion of the lane change assist; and (iii) atarget lane change time period which is a target time period from thestart of the lane change assist control until the completion of the lanechange assist control, and wherein the second calculation unit isconfigured to calculate, the target trajectory function representing thetarget lateral position of the own vehicle in accordance with the secondelapse time from the steering determination time point, based on: (i) alateral state amount at the steering determination time pointrepresenting a lateral position of the own vehicle at the steeringdetermination time point and a lateral movement state amount of the ownvehicle at the steering determination time point; (ii) the final targetlateral state amount representing the target lateral position at thecompletion of the lane change assist control and the target lateralmovement state amount at the completion of the lane change assistcontrol; and (iii) a target lane change remaining time period which is atarget remaining time period from the steering determination time pointuntil the completion of the lane change assist control.
 5. The lanechange assist apparatus according to claim 4, wherein the secondcalculation unit is configured to set the target remaining lane changetime period based on a remaining distance at the steering determinationtime point which is a distance required for having the own vehicle movein the lane width direction until the completion of the lane changeassist control.
 6. The lane change assist apparatus according to claim4, wherein the second calculation unit is configured to correct thetarget remaining lane change time period in such a manner that thetarget remaining lane change time period is shorter as a lateral speedin the lane width direction of the own vehicle at the steeringdetermination time point or a lateral acceleration in the lane widthdirection of the own vehicle at the steering determination time point ishigher.
 7. The lane change assist apparatus according to claim 2,wherein the second calculation unit is configured to calculate thetarget trajectory function up to once during one lane change assistcontrol.
 8. The lane change assist apparatus according to claim 2,wherein the second calculation unit is configured to at the steeringdetermination time point, calculate a deviation between the targetlateral position of the own vehicle obtained by the target trajectoryfunction calculated by the first calculation unit, and an actual lateralposition of the own vehicle detected by the lane recognition unit, andwhen the deviation is equal to or higher than a threshold and the actuallateral position is positioned at a position deviated in a lane changedirection with respect to the target lateral position, calculate thetarget trajectory function.
 9. The lane change assist apparatusaccording to claim 1, wherein the steering operation determination unitis configured to determine that the driver has performed the steeringoperation, when a steering torque input to a steering wheel by thedriver becomes equal to or higher than a first threshold for determininga start of the steering operation, and thereafter becomes equal to orlower than a second threshold for determining a termination of thesteering operation.